x86: fix kernel address printk exposures

PATCH In review Josh Poimboeuf 4 participants 17 messages Oct 25, 2016 – Nov 29, 2016

Subsystems (9)

Memory management Documentation x86 Page allocator +5 more subsystems

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Josh Poimboeuf

author

2016-10-25 14:51 UTC #0 lore raw

cover x86: fix kernel address printk exposures

These are some changes suggested by Linus to remove some kernel address exposures in printk. Most notably, the x86 stack dump no longer prints full kernel text addresses.

There's also a fix for the faddr2line script which is used for converting a function offset into a source code file name and line number.

Josh Poimboeuf (4):
scripts/faddr2line: fix "size mismatch" error x86/dumpstack: remove kernel text addresses from stack dump x86/dumpstack: remove raw stack dump
mm: remove kernel address exposure in free_reserved_area()

 Documentation/kernel-parameters.txt       |  3 --
 Documentation/sysctl/kernel.txt           |  8 -----
 Documentation/x86/x86_64/boot-options.txt |  4 ---
 arch/x86/include/asm/kdebug.h             |  1 -
 arch/x86/include/asm/stacktrace.h         |  5 ---
 arch/x86/kernel/dumpstack.c               | 39 ++++-------------------
 arch/x86/kernel/dumpstack_32.c            | 33 +------------------
 arch/x86/kernel/dumpstack_64.c            | 53 +------------------------------
 arch/x86/kernel/process_32.c              |  7 ++--
 arch/x86/kernel/process_64.c              |  6 ++--
 arch/x86/mm/fault.c                       |  3 +-
 arch/x86/platform/uv/uv_nmi.c             |  4 +--
 kernel/sysctl.c                           |  7 ----
 mm/page_alloc.c                           |  4 +--
 scripts/faddr2line                        | 33 ++++++++++++-------
 15 files changed, 40 insertions(+), 170 deletions(-)

Signature · 1 line

2.7.4

Josh Poimboeuf

author

2016-10-25 14:52 UTC #1 lore raw

PATCH 1/4 scripts/faddr2line: fix "size mismatch" error

I'm not sure how we missed this problem before. When I take a function address and size from an oops and give it to faddr2line, it usually complains about a size mismatch:

  $ scripts/faddr2line ~/k/vmlinux write_sysrq_trigger+0x51/0x60
  skipping write_sysrq_trigger address at 0xffffffff815731a1 due to size mismatch (0x60 != 83)
  no match for write_sysrq_trigger+0x51/0x60

The problem is caused by differences in how kallsyms and faddr2line determine a function's size.

kallsyms calculates a function's size by parsing the output of 'nm -n' and subtracting the next function's address from the current function's address. This means that nop instructions after the end of the function are included in the size.

In contrast, faddr2line reads the size from the symbol table, which does *not* include the ending nops in the function's size.

Change faddr2line to calculate the size from the output of 'nm -n' to be consistent with kallsyms and oops outputs.

Signed-off-by Josh Poimboeuf <[email protected]>

---
 scripts/faddr2line | 33 +++++++++++++++++++++------------
 1 file changed, 21 insertions(+), 12 deletions(-)

scripts/faddr2line +21 ~~-12~~

index 450b332..29df825 100755
@@ -105,9 +105,18 @@ __faddr2line() {
 	# In rare cases there might be duplicates.
 	while read symbol; do
 		local fields=($symbol)
-		local sym_base=0x${fields[1]}
-		local sym_size=${fields[2]}
-		local sym_type=${fields[3]}
+		local sym_base=0x${fields[0]}
+		local sym_type=${fields[1]}
+		local sym_end=0x${fields[3]}
+
+		# calculate the size
+		local sym_size=$(($sym_end - $sym_base))
+		if [[ -z $sym_size ]] || [[ $sym_size -le 0 ]]; then
+			warn "bad symbol size: base: $sym_base end: $sym_end"
+			DONE=1
+			return
+		fi
+		sym_size=0x$(printf %x $sym_size)
 
 		# calculate the address
 		local addr=$(($sym_base + $offset))

@@ -116,26 +125,26 @@ __faddr2line() {
 			DONE=1
 			return
 		fi
-		local hexaddr=0x$(printf %x $addr)
+		addr=0x$(printf %x $addr)
 
 		# weed out non-function symbols
-		if [[ $sym_type != "FUNC" ]]; then
+		if [[ $sym_type != t ]] && [[ $sym_type != T ]]; then
 			[[ $print_warnings = 1 ]] &&
-				echo "skipping $func address at $hexaddr due to non-function symbol"
+				echo "skipping $func address at $addr due to non-function symbol of type '$sym_type'"
 			continue
 		fi
 
 		# if the user provided a size, make sure it matches the symbol's size
 		if [[ -n $size ]] && [[ $size -ne $sym_size ]]; then
 			[[ $print_warnings = 1 ]] &&
-				echo "skipping $func address at $hexaddr due to size mismatch ($size != $sym_size)"
+				echo "skipping $func address at $addr due to size mismatch ($size != $sym_size)"
 			continue;
 		fi
 
 		# make sure the provided offset is within the symbol's range
 		if [[ $offset -gt $sym_size ]]; then
 			[[ $print_warnings = 1 ]] &&
-				echo "skipping $func address at $hexaddr due to size mismatch ($offset > $sym_size)"
+				echo "skipping $func address at $addr due to size mismatch ($offset > $sym_size)"
 			continue
 		fi

@@ -143,12 +152,12 @@ __faddr2line() {
 		[[ $FIRST = 0 ]] && echo
 		FIRST=0
 
-		local hexsize=0x$(printf %x $sym_size)
-		echo "$func+$offset/$hexsize:"
-		addr2line -fpie $objfile $hexaddr | sed "s; $dir_prefix\(\./\)*; ;"
+		# pass real address to addr2line
+		echo "$func+$offset/$sym_size:"
+		addr2line -fpie $objfile $addr | sed "s; $dir_prefix\(\./\)*; ;"
 		DONE=1
 
-	done < <(readelf -sW $objfile | awk -v f=$func '$8 == f {print}')
+	done < <(nm -n $objfile | awk -v fn=$func '$3 == fn { found=1; line=$0; start=$1; next } found == 1 { found=0; print line, $1 }')
 }
 
 [[ $# -lt 2 ]] && usage

Signature · 1 line

2.7.4

tip-bot for Josh Poimboeuf

merge bot

2016-10-26 05:42 UTC #2 lore raw

[tip:x86/asm] scripts/faddr2line: Fix "size mismatch" error

scripts/faddr2line: Fix "size mismatch" error

Commit-ID:  efdb4167e676aaba7505bec739785b76e206cb45
Gitweb:     http://git.kernel.org/tip/efdb4167e676aaba7505bec739785b76e206cb45
Author:     Josh Poimboeuf <[email protected]>
AuthorDate: Tue, 25 Oct 2016 09:51:11 -0500
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue, 25 Oct 2016 18:40:37 +0200

scripts/faddr2line: Fix "size mismatch" error

I'm not sure how we missed this problem before. When I take a function address and size from an oops and give it to faddr2line, it usually complains about a size mismatch:

  $ scripts/faddr2line ~/k/vmlinux write_sysrq_trigger+0x51/0x60
  skipping write_sysrq_trigger address at 0xffffffff815731a1 due to size mismatch (0x60 != 83)
  no match for write_sysrq_trigger+0x51/0x60

The problem is caused by differences in how kallsyms and faddr2line determine a function's size.

In contrast, faddr2line reads the size from the symbol table, which does *not* include the ending nops in the function's size.

Change faddr2line to calculate the size from the output of 'nm -n' to be consistent with kallsyms and oops outputs.

Signed-off-by Josh Poimboeuf <[email protected]>

Cc Andy Lutomirski <[email protected]>

Cc Borislav Petkov <[email protected]>

Cc Brian Gerst <[email protected]>

Cc Denys Vlasenko <[email protected]>

Cc H. Peter Anvin <[email protected]>

Cc Linus Torvalds <[email protected]>

Cc Peter Zijlstra <[email protected]>

Cc Thomas Gleixner <[email protected]>

Link http://lkml.kernel.org/r/bd313ed7c4003f6b1fda63e825325c44a9d837de.1477405374.git.jpoimboe@redhat.com open here

Signed-off-by Ingo Molnar <[email protected]>

---
 scripts/faddr2line | 33 +++++++++++++++++++++------------
 1 file changed, 21 insertions(+), 12 deletions(-)

scripts/faddr2line +21 ~~-12~~

index 450b332..29df825 100755
@@ -105,9 +105,18 @@ __faddr2line() {
 	# In rare cases there might be duplicates.
 	while read symbol; do
 		local fields=($symbol)
-		local sym_base=0x${fields[1]}
-		local sym_size=${fields[2]}
-		local sym_type=${fields[3]}
+		local sym_base=0x${fields[0]}
+		local sym_type=${fields[1]}
+		local sym_end=0x${fields[3]}
+
+		# calculate the size
+		local sym_size=$(($sym_end - $sym_base))
+		if [[ -z $sym_size ]] || [[ $sym_size -le 0 ]]; then
+			warn "bad symbol size: base: $sym_base end: $sym_end"
+			DONE=1
+			return
+		fi
+		sym_size=0x$(printf %x $sym_size)
 
 		# calculate the address
 		local addr=$(($sym_base + $offset))

@@ -116,26 +125,26 @@ __faddr2line() {
 			DONE=1
 			return
 		fi
-		local hexaddr=0x$(printf %x $addr)
+		addr=0x$(printf %x $addr)
 
 		# weed out non-function symbols
-		if [[ $sym_type != "FUNC" ]]; then
+		if [[ $sym_type != t ]] && [[ $sym_type != T ]]; then
 			[[ $print_warnings = 1 ]] &&
-				echo "skipping $func address at $hexaddr due to non-function symbol"
+				echo "skipping $func address at $addr due to non-function symbol of type '$sym_type'"
 			continue
 		fi
 
 		# if the user provided a size, make sure it matches the symbol's size
 		if [[ -n $size ]] && [[ $size -ne $sym_size ]]; then
 			[[ $print_warnings = 1 ]] &&
-				echo "skipping $func address at $hexaddr due to size mismatch ($size != $sym_size)"
+				echo "skipping $func address at $addr due to size mismatch ($size != $sym_size)"
 			continue;
 		fi
 
 		# make sure the provided offset is within the symbol's range
 		if [[ $offset -gt $sym_size ]]; then
 			[[ $print_warnings = 1 ]] &&
-				echo "skipping $func address at $hexaddr due to size mismatch ($offset > $sym_size)"
+				echo "skipping $func address at $addr due to size mismatch ($offset > $sym_size)"
 			continue
 		fi

@@ -143,12 +152,12 @@ __faddr2line() {
 		[[ $FIRST = 0 ]] && echo
 		FIRST=0
 
-		local hexsize=0x$(printf %x $sym_size)
-		echo "$func+$offset/$hexsize:"
-		addr2line -fpie $objfile $hexaddr | sed "s; $dir_prefix\(\./\)*; ;"
+		# pass real address to addr2line
+		echo "$func+$offset/$sym_size:"
+		addr2line -fpie $objfile $addr | sed "s; $dir_prefix\(\./\)*; ;"
 		DONE=1
 
-	done < <(readelf -sW $objfile | awk -v f=$func '$8 == f {print}')
+	done < <(nm -n $objfile | awk -v fn=$func '$3 == fn { found=1; line=$0; start=$1; next } found == 1 { found=0; print line, $1 }')
 }
 
 [[ $# -lt 2 ]] && usage

Josh Poimboeuf

author

2016-10-25 14:51 UTC #3 lore raw

PATCH 2/4 x86/dumpstack: remove kernel text addresses from stack dump

In reply to Josh Poimboeuf

Printing kernel text addresses in stack dumps is of questionable value, especially now that address randomization is becoming common.

It can be a security issue because it leaks kernel addresses. It also affects the usefulness of the stack dump. Linus says:

"I actually spend time cleaning up commit messages in logs, because useless data that isn't actually information (random hex numbers) is actively detrimental.

It makes commit logs less legible.

It also makes it harder to parse dumps.

It's not useful. That makes it actively bad.

I probably look at more oops reports than most people. I have not found the hex numbers useful for the last five years, because they are just randomized crap.

The stack content thing just makes code scroll off the screen etc, for example."

The only real downside to removing these addresses is that they can be used to disambiguate duplicate symbol names. However such cases are rare, and the context of the stack dump should be enough to be able to figure it out.

There's now a 'faddr2line' script which can be used to convert a function address to a file name and line:

  $ ./scripts/faddr2line ~/k/vmlinux write_sysrq_trigger+0x51/0x60
  write_sysrq_trigger+0x51/0x60:
  write_sysrq_trigger at drivers/tty/sysrq.c:1098

Or gdb can be used:

  $ echo "list *write_sysrq_trigger+0x51" |gdb ~/k/vmlinux |grep "is in"
  (gdb) 0xffffffff815b5d83 is in driver_probe_device (/home/jpoimboe/git/linux/drivers/base/dd.c:378).

(But note that when there are duplicate symbol names, gdb will only show the first symbol it finds. faddr2line is recommended over gdb because it handles duplicates and it also does function size checking.)

Here's an example of what a stack dump looks like after this change:

  BUG: unable to handle kernel NULL pointer dereference at           (null)
  IP: sysrq_handle_crash+0x45/0x80
  PGD 36bfa067 [   29.650644] PUD 7aca3067
 50970]
  Oops: 0002 [#1] PREEMPT SMP
  Modules linked in: ...
  CPU: 1 PID: 786 Comm: bash Tainted: G            E   4.9.0-rc1+ #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.1-1.fc24 04/01/2014
  task: ffff880078582a40 task.stack: ffffc90000ba8000
  RIP: 0010:sysrq_handle_crash+0x45/0x80
  RSP: 0018:ffffc90000babdc8 EFLAGS: 00010296
  RAX: ffff880078582a40 RBX: 0000000000000063 RCX: 0000000000000001
  RDX: 0000000000000001 RSI: 0000000000000000 RDI: 0000000000000292
  RBP: ffffc90000babdc8 R08: 0000000b31866061 R09: 0000000000000000
  R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
  R13: 0000000000000007 R14: ffffffff81ee8680 R15: 0000000000000000
  FS:  00007ffb43869700(0000) GS:ffff88007d400000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000000 CR3: 000000007a3e9000 CR4: 00000000001406e0
  Stack:
   ffffc90000babe00 ffffffff81572d08 ffffffff81572bd5 0000000000000002
   0000000000000000 ffff880079606600 00007ffb4386e000 ffffc90000babe20
   ffffffff81573201 ffff880036a3fd00 fffffffffffffffb ffffc90000babe40
  Call Trace:
   __handle_sysrq+0x138/0x220
   ? __handle_sysrq+0x5/0x220
   write_sysrq_trigger+0x51/0x60
   proc_reg_write+0x42/0x70
   __vfs_write+0x37/0x140
   ? preempt_count_sub+0xa1/0x100
   ? __sb_start_write+0xf5/0x210
   ? vfs_write+0x183/0x1a0
   vfs_write+0xb8/0x1a0
   SyS_write+0x58/0xc0
   entry_SYSCALL_64_fastpath+0x1f/0xc2
  RIP: 0033:0x7ffb42f55940
  RSP: 002b:00007ffd33bb6b18 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
  RAX: ffffffffffffffda RBX: 0000000000000046 RCX: 00007ffb42f55940
  RDX: 0000000000000002 RSI: 00007ffb4386e000 RDI: 0000000000000001
  RBP: 0000000000000011 R08: 00007ffb4321ea40 R09: 00007ffb43869700
  R10: 00007ffb43869700 R11: 0000000000000246 R12: 0000000000778a10
  R13: 00007ffd33bb5c00 R14: 0000000000000007 R15: 0000000000000010
  Code: 34 e8 d0 34 bc ff 48 c7 c2 3b 2b 57 81 be 01 00 00 00 48 c7 c7 e0 dd e5 81 e8 a8 55 ba ff c7 05 0e 3f de 00 01 00 00 00 0f ae f8 <c6> 04 25 00 00 00 00 01 5d c3 e8 4c 49 bc ff 84 c0 75 c3 48 c7
  RIP: sysrq_handle_crash+0x45/0x80 RSP: ffffc90000babdc8
  CR2: 0000000000000000

Signed-off-by Josh Poimboeuf <[email protected]>

---
 arch/x86/include/asm/kdebug.h |  1 -
 arch/x86/kernel/dumpstack.c   | 18 ++++--------------
 arch/x86/kernel/process_32.c  |  7 +++----
 arch/x86/kernel/process_64.c  |  6 +++---
 arch/x86/mm/fault.c           |  3 +--
 arch/x86/platform/uv/uv_nmi.c |  4 ++--
 6 files changed, 13 insertions(+), 26 deletions(-)

arch/x86/include/asm/kdebug.h +0 -1

index d318811..29a594a 100644
@@ -21,7 +21,6 @@ enum die_val {
 	DIE_NMIUNKNOWN,
 };
 
-extern void printk_address(unsigned long address);
 extern void die(const char *, struct pt_regs *,long);
 extern int __must_check __die(const char *, struct pt_regs *, long);
 extern void show_stack_regs(struct pt_regs *regs);

arch/x86/kernel/dumpstack.c +4 ~~-14~~

index 64281a1..f967652 100644
@@ -46,14 +46,7 @@ static void printk_stack_address(unsigned long address, int reliable,
 				 char *log_lvl)
 {
 	touch_nmi_watchdog();
-	printk("%s [<%p>] %s%pB\n",
-		log_lvl, (void *)address, reliable ? "" : "? ",
-		(void *)address);
-}
-
-void printk_address(unsigned long address)
-{
-	pr_cont(" [<%p>] %pS\n", (void *)address, (void *)address);
+	printk("%s %s%pB\n", log_lvl, reliable ? "" : "? ", (void *)address);
 }
 
 void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,

@@ -275,14 +268,11 @@ int __die(const char *str, struct pt_regs *regs, long err)
 		sp = kernel_stack_pointer(regs);
 		savesegment(ss, ss);
 	}
-	printk(KERN_EMERG "EIP: [<%08lx>] ", regs->ip);
-	print_symbol("%s", regs->ip);
-	printk(" SS:ESP %04x:%08lx\n", ss, sp);
+	printk(KERN_EMERG "EIP: %pS SS:ESP: %04x:%08lx\n",
+	       (void *)regs->ip, ss, sp);
 #else
 	/* Executive summary in case the oops scrolled away */
-	printk(KERN_ALERT "RIP ");
-	printk_address(regs->ip);
-	printk(" RSP <%016lx>\n", regs->sp);
+	printk(KERN_ALERT "RIP: %pS RSP: %016lx\n", (void *)regs->ip, regs->sp);
 #endif
 	return 0;
 }

arch/x86/kernel/process_32.c +3 -4

index 7dc8c9c..f854404 100644
@@ -72,10 +72,9 @@ void __show_regs(struct pt_regs *regs, int all)
 		savesegment(gs, gs);
 	}
 
-	printk(KERN_DEFAULT "EIP: %04x:[<%08lx>] EFLAGS: %08lx CPU: %d\n",
-			(u16)regs->cs, regs->ip, regs->flags,
-			smp_processor_id());
-	print_symbol("EIP is at %s\n", regs->ip);
+	printk(KERN_DEFAULT "EIP: %pS\n", (void *)regs->ip);
+	printk(KERN_DEFAULT "EFLAGS: %08lx CPU: %d\n", regs->flags,
+		smp_processor_id());
 
 	printk(KERN_DEFAULT "EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
 		regs->ax, regs->bx, regs->cx, regs->dx);

arch/x86/kernel/process_64.c +3 -3

index 4481e72..6c1b43e 100644
@@ -61,10 +61,10 @@ void __show_regs(struct pt_regs *regs, int all)
 	unsigned int fsindex, gsindex;
 	unsigned int ds, cs, es;
 
-	printk(KERN_DEFAULT "RIP: %04lx:[<%016lx>] %pS\n", regs->cs & 0xffff,
-			regs->ip, (void *)regs->ip);
+	printk(KERN_DEFAULT "RIP: %04lx:%pS\n", regs->cs & 0xffff,
+		(void *)regs->ip);
 	printk(KERN_DEFAULT "RSP: %04lx:%016lx EFLAGS: %08lx", regs->ss,
-			regs->sp, regs->flags);
+		regs->sp, regs->flags);
 	if (regs->orig_ax != -1)
 		pr_cont(" ORIG_RAX: %016lx\n", regs->orig_ax);
 	else

arch/x86/mm/fault.c +1 -2

index 9f72ca3..17c55a5 100644
@@ -679,8 +679,7 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code,
 		printk(KERN_CONT "paging request");
 
 	printk(KERN_CONT " at %p\n", (void *) address);
-	printk(KERN_ALERT "IP:");
-	printk_address(regs->ip);
+	printk(KERN_ALERT "IP: %pS\n", (void *)regs->ip);
 
 	dump_pagetable(address);
 }

arch/x86/platform/uv/uv_nmi.c +2 -2

index cd5173a..8410e7d 100644
@@ -387,8 +387,8 @@ static void uv_nmi_dump_cpu_ip_hdr(void)
 /* Dump Instruction Pointer info */
 static void uv_nmi_dump_cpu_ip(int cpu, struct pt_regs *regs)
 {
-	pr_info("UV: %4d %6d %-32.32s ", cpu, current->pid, current->comm);
-	printk_address(regs->ip);
+	pr_info("UV: %4d %6d %-32.32s %pS",
+		cpu, current->pid, current->comm, (void *)regs->ip);
 }
 
 /*

Signature · 1 line

2.7.4

tip-bot for Josh Poimboeuf

merge bot

2016-10-26 05:42 UTC #4 lore raw

[tip:x86/asm] x86/dumpstack: Remove kernel text addresses from stack dump

x86/dumpstack: Remove kernel text addresses from stack dump

Commit-ID:  bb5e5ce545f2031c96f7901cd8d1698ea3ca4c9c
Gitweb:     http://git.kernel.org/tip/bb5e5ce545f2031c96f7901cd8d1698ea3ca4c9c
Author:     Josh Poimboeuf <[email protected]>
AuthorDate: Tue, 25 Oct 2016 09:51:12 -0500
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue, 25 Oct 2016 18:40:37 +0200

x86/dumpstack: Remove kernel text addresses from stack dump

Printing kernel text addresses in stack dumps is of questionable value, especially now that address randomization is becoming common.

It can be a security issue because it leaks kernel addresses. It also affects the usefulness of the stack dump. Linus says:

"I actually spend time cleaning up commit messages in logs, because useless data that isn't actually information (random hex numbers) is actively detrimental.

It makes commit logs less legible.

It also makes it harder to parse dumps.

It's not useful. That makes it actively bad.

I probably look at more oops reports than most people. I have not found the hex numbers useful for the last five years, because they are just randomized crap.

The stack content thing just makes code scroll off the screen etc, for example."

There's now a 'faddr2line' script which can be used to convert a function address to a file name and line:

  $ ./scripts/faddr2line ~/k/vmlinux write_sysrq_trigger+0x51/0x60
  write_sysrq_trigger+0x51/0x60:
  write_sysrq_trigger at drivers/tty/sysrq.c:1098

Or gdb can be used:

  $ echo "list *write_sysrq_trigger+0x51" |gdb ~/k/vmlinux |grep "is in"
  (gdb) 0xffffffff815b5d83 is in driver_probe_device (/home/jpoimboe/git/linux/drivers/base/dd.c:378).

Here's an example of what a stack dump looks like after this change:

  BUG: unable to handle kernel NULL pointer dereference at           (null)
  IP: sysrq_handle_crash+0x45/0x80
  PGD 36bfa067 [   29.650644] PUD 7aca3067
  Oops: 0002 [#1] PREEMPT SMP
  Modules linked in: ...
  CPU: 1 PID: 786 Comm: bash Tainted: G            E   4.9.0-rc1+ #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.1-1.fc24 04/01/2014
  task: ffff880078582a40 task.stack: ffffc90000ba8000
  RIP: 0010:sysrq_handle_crash+0x45/0x80
  RSP: 0018:ffffc90000babdc8 EFLAGS: 00010296
  RAX: ffff880078582a40 RBX: 0000000000000063 RCX: 0000000000000001
  RDX: 0000000000000001 RSI: 0000000000000000 RDI: 0000000000000292
  RBP: ffffc90000babdc8 R08: 0000000b31866061 R09: 0000000000000000
  R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
  R13: 0000000000000007 R14: ffffffff81ee8680 R15: 0000000000000000
  FS:  00007ffb43869700(0000) GS:ffff88007d400000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000000 CR3: 000000007a3e9000 CR4: 00000000001406e0
  Stack:
   ffffc90000babe00 ffffffff81572d08 ffffffff81572bd5 0000000000000002
   0000000000000000 ffff880079606600 00007ffb4386e000 ffffc90000babe20
   ffffffff81573201 ffff880036a3fd00 fffffffffffffffb ffffc90000babe40
  Call Trace:
   __handle_sysrq+0x138/0x220
   ? __handle_sysrq+0x5/0x220
   write_sysrq_trigger+0x51/0x60
   proc_reg_write+0x42/0x70
   __vfs_write+0x37/0x140
   ? preempt_count_sub+0xa1/0x100
   ? __sb_start_write+0xf5/0x210
   ? vfs_write+0x183/0x1a0
   vfs_write+0xb8/0x1a0
   SyS_write+0x58/0xc0
   entry_SYSCALL_64_fastpath+0x1f/0xc2
  RIP: 0033:0x7ffb42f55940
  RSP: 002b:00007ffd33bb6b18 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
  RAX: ffffffffffffffda RBX: 0000000000000046 RCX: 00007ffb42f55940
  RDX: 0000000000000002 RSI: 00007ffb4386e000 RDI: 0000000000000001
  RBP: 0000000000000011 R08: 00007ffb4321ea40 R09: 00007ffb43869700
  R10: 00007ffb43869700 R11: 0000000000000246 R12: 0000000000778a10
  R13: 00007ffd33bb5c00 R14: 0000000000000007 R15: 0000000000000010
  Code: 34 e8 d0 34 bc ff 48 c7 c2 3b 2b 57 81 be 01 00 00 00 48 c7 c7 e0 dd e5 81 e8 a8 55 ba ff c7 05 0e 3f de 00 01 00 00 00 0f ae f8 <c6> 04 25 00 00 00 00 01 5d c3 e8 4c 49 bc ff 84 c0 75 c3 48 c7
  RIP: sysrq_handle_crash+0x45/0x80 RSP: ffffc90000babdc8
  CR2: 0000000000000000

Signed-off-by Josh Poimboeuf <[email protected]>

Cc Andy Lutomirski <[email protected]>

Cc Borislav Petkov <[email protected]>

Cc Brian Gerst <[email protected]>

Cc Denys Vlasenko <[email protected]>

Cc H. Peter Anvin <[email protected]>

Cc Peter Zijlstra <[email protected]>

Cc Thomas Gleixner <[email protected]>

Link http://lkml.kernel.org/r/69329cb29b8f324bb5fcea14d61d224807fb6488.1477405374.git.jpoimboe@redhat.com open here

Signed-off-by Ingo Molnar <[email protected]>

---
 arch/x86/include/asm/kdebug.h |  1 -
 arch/x86/kernel/dumpstack.c   | 18 ++++--------------
 arch/x86/kernel/process_32.c  |  7 +++----
 arch/x86/kernel/process_64.c  |  6 +++---
 arch/x86/mm/fault.c           |  3 +--
 arch/x86/platform/uv/uv_nmi.c |  4 ++--
 6 files changed, 13 insertions(+), 26 deletions(-)

arch/x86/include/asm/kdebug.h +0 -1

index d318811..29a594a 100644
@@ -21,7 +21,6 @@ enum die_val {
 	DIE_NMIUNKNOWN,
 };
 
-extern void printk_address(unsigned long address);
 extern void die(const char *, struct pt_regs *,long);
 extern int __must_check __die(const char *, struct pt_regs *, long);
 extern void show_stack_regs(struct pt_regs *regs);

arch/x86/kernel/dumpstack.c +4 ~~-14~~

index 64281a1..f967652 100644
@@ -46,14 +46,7 @@ static void printk_stack_address(unsigned long address, int reliable,
 				 char *log_lvl)
 {
 	touch_nmi_watchdog();
-	printk("%s [<%p>] %s%pB\n",
-		log_lvl, (void *)address, reliable ? "" : "? ",
-		(void *)address);
-}
-
-void printk_address(unsigned long address)
-{
-	pr_cont(" [<%p>] %pS\n", (void *)address, (void *)address);
+	printk("%s %s%pB\n", log_lvl, reliable ? "" : "? ", (void *)address);
 }
 
 void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,

@@ -275,14 +268,11 @@ int __die(const char *str, struct pt_regs *regs, long err)
 		sp = kernel_stack_pointer(regs);
 		savesegment(ss, ss);
 	}
-	printk(KERN_EMERG "EIP: [<%08lx>] ", regs->ip);
-	print_symbol("%s", regs->ip);
-	printk(" SS:ESP %04x:%08lx\n", ss, sp);
+	printk(KERN_EMERG "EIP: %pS SS:ESP: %04x:%08lx\n",
+	       (void *)regs->ip, ss, sp);
 #else
 	/* Executive summary in case the oops scrolled away */
-	printk(KERN_ALERT "RIP ");
-	printk_address(regs->ip);
-	printk(" RSP <%016lx>\n", regs->sp);
+	printk(KERN_ALERT "RIP: %pS RSP: %016lx\n", (void *)regs->ip, regs->sp);
 #endif
 	return 0;
 }

arch/x86/kernel/process_32.c +3 -4

index bd7be8e..e3223bc 100644
@@ -72,10 +72,9 @@ void __show_regs(struct pt_regs *regs, int all)
 		savesegment(gs, gs);
 	}
 
-	printk(KERN_DEFAULT "EIP: %04x:[<%08lx>] EFLAGS: %08lx CPU: %d\n",
-			(u16)regs->cs, regs->ip, regs->flags,
-			smp_processor_id());
-	print_symbol("EIP is at %s\n", regs->ip);
+	printk(KERN_DEFAULT "EIP: %pS\n", (void *)regs->ip);
+	printk(KERN_DEFAULT "EFLAGS: %08lx CPU: %d\n", regs->flags,
+		smp_processor_id());
 
 	printk(KERN_DEFAULT "EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
 		regs->ax, regs->bx, regs->cx, regs->dx);

arch/x86/kernel/process_64.c +3 -3

index f1c36da..c99f1ca 100644
@@ -61,10 +61,10 @@ void __show_regs(struct pt_regs *regs, int all)
 	unsigned int fsindex, gsindex;
 	unsigned int ds, cs, es;
 
-	printk(KERN_DEFAULT "RIP: %04lx:[<%016lx>] %pS\n", regs->cs & 0xffff,
-			regs->ip, (void *)regs->ip);
+	printk(KERN_DEFAULT "RIP: %04lx:%pS\n", regs->cs & 0xffff,
+		(void *)regs->ip);
 	printk(KERN_DEFAULT "RSP: %04lx:%016lx EFLAGS: %08lx", regs->ss,
-			regs->sp, regs->flags);
+		regs->sp, regs->flags);
 	if (regs->orig_ax != -1)
 		pr_cont(" ORIG_RAX: %016lx\n", regs->orig_ax);
 	else

arch/x86/mm/fault.c +1 -2

index 9f72ca3..17c55a5 100644
@@ -679,8 +679,7 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code,
 		printk(KERN_CONT "paging request");
 
 	printk(KERN_CONT " at %p\n", (void *) address);
-	printk(KERN_ALERT "IP:");
-	printk_address(regs->ip);
+	printk(KERN_ALERT "IP: %pS\n", (void *)regs->ip);
 
 	dump_pagetable(address);
 }

arch/x86/platform/uv/uv_nmi.c +2 -2

index cd5173a..8410e7d 100644
@@ -387,8 +387,8 @@ static void uv_nmi_dump_cpu_ip_hdr(void)
 /* Dump Instruction Pointer info */
 static void uv_nmi_dump_cpu_ip(int cpu, struct pt_regs *regs)
 {
-	pr_info("UV: %4d %6d %-32.32s ", cpu, current->pid, current->comm);
-	printk_address(regs->ip);
+	pr_info("UV: %4d %6d %-32.32s %pS",
+		cpu, current->pid, current->comm, (void *)regs->ip);
 }
 
 /*

Kirill A. Shutemov

2016-11-25 12:26 UTC #5 lore raw

Re: [PATCH 2/4] x86/dumpstack: remove kernel text addresses from stack dump

In reply to Josh Poimboeuf

Quoted 35 lines · Josh Poimboeuf

Printing kernel text addresses in stack dumps is of questionable value, especially now that address randomization is becoming common.
It can be a security issue because it leaks kernel addresses. It also affects the usefulness of the stack dump. Linus says:
"I actually spend time cleaning up commit messages in logs, because useless data that isn't actually information (random hex numbers) is actively detrimental.
It makes commit logs less legible.
It also makes it harder to parse dumps.
It's not useful. That makes it actively bad.
I probably look at more oops reports than most people. I have not found the hex numbers useful for the last five years, because they are just randomized crap.
The stack content thing just makes code scroll off the screen etc, for example."
The only real downside to removing these addresses is that they can be used to disambiguate duplicate symbol names. However such cases are rare, and the context of the stack dump should be enough to be able to figure it out.
There's now a 'faddr2line' script which can be used to convert a function address to a file name and line:
  $ ./scripts/faddr2line ~/k/vmlinux write_sysrq_trigger+0x51/0x60
  write_sysrq_trigger+0x51/0x60:
  write_sysrq_trigger at drivers/tty/sysrq.c:1098

Quoted 8 lines

Or gdb can be used:
  $ echo "list *write_sysrq_trigger+0x51" |gdb ~/k/vmlinux |grep "is in"
  (gdb) 0xffffffff815b5d83 is in driver_probe_device (/home/jpoimboe/git/linux/drivers/base/dd.c:378).
(But note that when there are duplicate symbol names, gdb will only show the first symbol it finds. faddr2line is recommended over gdb because it handles duplicates and it also does function size checking.)

The commit breaks scripts/decode_stacktrace.sh.

Not sure if it's possible to fix it only on decode_stacktrace.sh side: we seems don't have a way to clearly distinguish stack trace line of any other.

May be we should mark stack lines with some prefix to simplify decoding?

Signature · 1 line

 Kirill A. Shutemov

Josh Poimboeuf

author

2016-11-28 20:50 UTC #6 lore raw

Re: [PATCH 2/4] x86/dumpstack: remove kernel text addresses from stack dump

Quoted 45 lines · Kirill A. Shutemov

Quoted 35 lines · Josh Poimboeuf
Printing kernel text addresses in stack dumps is of questionable value, especially now that address randomization is becoming common.
It can be a security issue because it leaks kernel addresses. It also affects the usefulness of the stack dump. Linus says:
"I actually spend time cleaning up commit messages in logs, because useless data that isn't actually information (random hex numbers) is actively detrimental.
It makes commit logs less legible.
It also makes it harder to parse dumps.
It's not useful. That makes it actively bad.
I probably look at more oops reports than most people. I have not found the hex numbers useful for the last five years, because they are just randomized crap.
The stack content thing just makes code scroll off the screen etc, for example."
The only real downside to removing these addresses is that they can be used to disambiguate duplicate symbol names. However such cases are rare, and the context of the stack dump should be enough to be able to figure it out.
There's now a 'faddr2line' script which can be used to convert a function address to a file name and line:
  $ ./scripts/faddr2line ~/k/vmlinux write_sysrq_trigger+0x51/0x60
  write_sysrq_trigger+0x51/0x60:
  write_sysrq_trigger at drivers/tty/sysrq.c:1098
Quoted 8 lines
Or gdb can be used:
  $ echo "list *write_sysrq_trigger+0x51" |gdb ~/k/vmlinux |grep "is in"
  (gdb) 0xffffffff815b5d83 is in driver_probe_device (/home/jpoimboe/git/linux/drivers/base/dd.c:378).
(But note that when there are duplicate symbol names, gdb will only show the first symbol it finds. faddr2line is recommended over gdb because it handles duplicates and it also does function size checking.)

Quoted 5 lines

The commit breaks scripts/decode_stacktrace.sh.
Not sure if it's possible to fix it only on decode_stacktrace.sh side: we seems don't have a way to clearly distinguish stack trace line of any other.

How about this bash regex? Seems to work for me with no false positives.

[[ $line =~ [^+\ ]+\+0x[0-9a-f]+/0x[0-9a-f]+ ]]

Signature · 1 line

Josh

Kirill A. Shutemov

2016-11-28 22:27 UTC #7 lore raw

Re: [PATCH 2/4] x86/dumpstack: remove kernel text addresses from stack dump

Quoted 48 lines · Josh Poimboeuf

Quoted 47 lines · Kirill A. Shutemov
Quoted 35 lines · Josh Poimboeuf
Printing kernel text addresses in stack dumps is of questionable value, especially now that address randomization is becoming common.
It can be a security issue because it leaks kernel addresses. It also affects the usefulness of the stack dump. Linus says:
"I actually spend time cleaning up commit messages in logs, because useless data that isn't actually information (random hex numbers) is actively detrimental.
It makes commit logs less legible.
It also makes it harder to parse dumps.
It's not useful. That makes it actively bad.
I probably look at more oops reports than most people. I have not found the hex numbers useful for the last five years, because they are just randomized crap.
The stack content thing just makes code scroll off the screen etc, for example."
The only real downside to removing these addresses is that they can be used to disambiguate duplicate symbol names. However such cases are rare, and the context of the stack dump should be enough to be able to figure it out.
There's now a 'faddr2line' script which can be used to convert a function address to a file name and line:
  $ ./scripts/faddr2line ~/k/vmlinux write_sysrq_trigger+0x51/0x60
  write_sysrq_trigger+0x51/0x60:
  write_sysrq_trigger at drivers/tty/sysrq.c:1098
Quoted 8 lines
Or gdb can be used:
  $ echo "list *write_sysrq_trigger+0x51" |gdb ~/k/vmlinux |grep "is in"
  (gdb) 0xffffffff815b5d83 is in driver_probe_device (/home/jpoimboe/git/linux/drivers/base/dd.c:378).
(But note that when there are duplicate symbol names, gdb will only show the first symbol it finds. faddr2line is recommended over gdb because it handles duplicates and it also does function size checking.)
The commit breaks scripts/decode_stacktrace.sh.

Quoted 8 lines

Quoted 3 lines
Not sure if it's possible to fix it only on decode_stacktrace.sh side: we seems don't have a way to clearly distinguish stack trace line of any other.
How about this bash regex? Seems to work for me with no false positives.
[[ $line =~ [^+\ ]+\+0x[0-9a-f]+/0x[0-9a-f]+ ]]

Seems works fine to me. Thanks.

Feel free to use my tested-by.

Signature · 1 line

 Kirill A. Shutemov

Josh Poimboeuf

author

2016-11-28 23:07 UTC #8 lore raw

PATCH 1/1 decode_stacktrace: fix address line detection on x86

Kirill reported that the decode_stacktrace.sh script was broken by the following commit:

bb5e5ce545f2 ("x86/dumpstack: Remove kernel text addresses from stack dump")

Fix it by updating the per-line absolute address check to also check for function-based address lines like the following:

write_sysrq_trigger+0x51/0x60

I didn't remove the check for absolute addresses because it's still needed for ARM.

Fixes bb5e5ce545f2 ("x86/dumpstack: Remove kernel text addresses from stack dump")

Reported-by "Kirill A. Shutemov" <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

---
 scripts/decode_stacktrace.sh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

scripts/decode_stacktrace.sh +2 -1

index c332684..5206d99 100755
@@ -139,7 +139,8 @@ handle_line() {
 
 while read line; do
 	# Let's see if we have an address in the line
-	if [[ $line =~ \[\<([^]]+)\>\]  ]]; then
+	if [[ $line =~ \[\<([^]]+)\>\] ]] ||
+	   [[ $line =~ [^+\ ]+\+0x[0-9a-f]+/0x[0-9a-f]+ ]]; then
 		# Translate address to line numbers
 		handle_line "$line"
 	# Is it a code line?

Signature · 1 line

2.7.4

tip-bot for Josh Poimboeuf

merge bot

2016-11-29 07:14 UTC #9 lore raw

[tip:x86/urgent] tools/decode_stacktrace.sh: Fix address line detection on x86

tools/decode_stacktrace.sh: Fix address line detection on x86

Commit-ID:  8e8d8725d46d93ceffd3e708d905bc101a1905b5
Gitweb:     http://git.kernel.org/tip/8e8d8725d46d93ceffd3e708d905bc101a1905b5
Author:     Josh Poimboeuf <[email protected]>
AuthorDate: Mon, 28 Nov 2016 17:06:35 -0600
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue, 29 Nov 2016 08:10:05 +0100

tools/decode_stacktrace.sh: Fix address line detection on x86

Kirill reported that the decode_stacktrace.sh script was broken by the following commit:

bb5e5ce545f2 ("x86/dumpstack: Remove kernel text addresses from stack dump")

Fix it by updating the per-line absolute address check to also check for function-based address lines like the following:

write_sysrq_trigger+0x51/0x60

I didn't remove the check for absolute addresses because it's still needed for ARM.

Reported-by Kirill A. Shutemov <[email protected]>

Tested-by Kirill A. Shutemov <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

Cc Konstantin Khlebnikov <[email protected]>

Cc Linus Torvalds <[email protected]>

Cc Peter Zijlstra <[email protected]>

Cc Sasha Levin <[email protected]>

Cc Thomas Gleixner <[email protected]>

Fixes bb5e5ce545f2 ("x86/dumpstack: Remove kernel text addresses from stack dump")

Link http://lkml.kernel.org/r/20161128230635.4n2ofgawltgexgcg@treble open here

Signed-off-by Ingo Molnar <[email protected]>

---
 scripts/decode_stacktrace.sh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

scripts/decode_stacktrace.sh +2 -1

index c332684..5206d99 100755
@@ -139,7 +139,8 @@ handle_line() {
 
 while read line; do
 	# Let's see if we have an address in the line
-	if [[ $line =~ \[\<([^]]+)\>\]  ]]; then
+	if [[ $line =~ \[\<([^]]+)\>\] ]] ||
+	   [[ $line =~ [^+\ ]+\+0x[0-9a-f]+/0x[0-9a-f]+ ]]; then
 		# Translate address to line numbers
 		handle_line "$line"
 	# Is it a code line?

Josh Poimboeuf

author

2016-11-29 13:06 UTC #10 lore raw

Re: [tip:x86/urgent] tools/decode_stacktrace.sh: Fix address line detection on x86

Hi tip-bot,

Quoted 8 lines · tip-bot for Josh Poimboeuf

Commit-ID:  8e8d8725d46d93ceffd3e708d905bc101a1905b5
Gitweb:     http://git.kernel.org/tip/8e8d8725d46d93ceffd3e708d905bc101a1905b5
Author:     Josh Poimboeuf <[email protected]>
AuthorDate: Mon, 28 Nov 2016 17:06:35 -0600
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue, 29 Nov 2016 08:10:05 +0100

tools/decode_stacktrace.sh: Fix address line detection on x86

It's actually in the scripts subdir, so: s/tools/scripts/

Also, while it should be harmless for this to be in 'urgent', I think it isn't necessary because it fixes a commit which is currently only in tip.

Signature · 1 line

Josh

Ingo Molnar

2016-11-29 13:20 UTC #11 lore raw

Re: [tip:x86/urgent] tools/decode_stacktrace.sh: Fix address line detection on x86

Quoted 10 lines · Josh Poimboeuf

Hi tip-bot,

Quoted 7 lines · tip-bot for Josh Poimboeuf

Commit-ID:  8e8d8725d46d93ceffd3e708d905bc101a1905b5
Gitweb:     http://git.kernel.org/tip/8e8d8725d46d93ceffd3e708d905bc101a1905b5
Author:     Josh Poimboeuf <[email protected]>
AuthorDate: Mon, 28 Nov 2016 17:06:35 -0600
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue, 29 Nov 2016 08:10:05 +0100

Quoted 3 lines

Quoted 1 line
tools/decode_stacktrace.sh: Fix address line detection on x86
It's actually in the scripts subdir, so: s/tools/scripts/

So that was conscious - it might be in 'scripts' but it is really a tool!

No strong feelings either way.

Quoted 3 lines

Also, while it should be harmless for this to be in 'urgent', I think it isn't necessary because it fixes a commit which is currently only in tip.

I missed that.

Ok, I rebased it over into tip:x86/asm and fixed the title as well while at it.

Thanks,

Ingo

tip-bot for Josh Poimboeuf

merge bot

2016-11-29 14:14 UTC #12 lore raw

[tip:x86/asm] scripts/decode_stacktrace.sh: Fix address line detection on x86

In reply to Josh Poimboeuf

scripts/decode_stacktrace.sh: Fix address line detection on x86

Commit-ID:  53938ee427bf27525a63721b7e25d86b8f31f161
Gitweb:     http://git.kernel.org/tip/53938ee427bf27525a63721b7e25d86b8f31f161
Author:     Josh Poimboeuf <[email protected]>
AuthorDate: Mon, 28 Nov 2016 17:06:35 -0600
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue, 29 Nov 2016 14:19:50 +0100

scripts/decode_stacktrace.sh: Fix address line detection on x86

Kirill reported that the decode_stacktrace.sh script was broken by the following commit:

bb5e5ce545f2 ("x86/dumpstack: Remove kernel text addresses from stack dump")

Fix it by updating the per-line absolute address check to also check for function-based address lines like the following:

write_sysrq_trigger+0x51/0x60

I didn't remove the check for absolute addresses because it's still needed for ARM.

Reported-by Kirill A. Shutemov <[email protected]>

Tested-by Kirill A. Shutemov <[email protected]>

Signed-off-by Josh Poimboeuf <[email protected]>

Cc Konstantin Khlebnikov <[email protected]>

Cc Linus Torvalds <[email protected]>

Cc Peter Zijlstra <[email protected]>

Cc Sasha Levin <[email protected]>

Cc Thomas Gleixner <[email protected]>

Fixes bb5e5ce545f2 ("x86/dumpstack: Remove kernel text addresses from stack dump")

Link http://lkml.kernel.org/r/20161128230635.4n2ofgawltgexgcg@treble open here

Signed-off-by Ingo Molnar <[email protected]>

---
 scripts/decode_stacktrace.sh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

scripts/decode_stacktrace.sh +2 -1

index c332684..5206d99 100755
@@ -139,7 +139,8 @@ handle_line() {
 
 while read line; do
 	# Let's see if we have an address in the line
-	if [[ $line =~ \[\<([^]]+)\>\]  ]]; then
+	if [[ $line =~ \[\<([^]]+)\>\] ]] ||
+	   [[ $line =~ [^+\ ]+\+0x[0-9a-f]+/0x[0-9a-f]+ ]]; then
 		# Translate address to line numbers
 		handle_line "$line"
 	# Is it a code line?

Josh Poimboeuf

author

2016-10-25 14:51 UTC #13 lore raw

PATCH 3/4 x86/dumpstack: remove raw stack dump

In reply to Josh Poimboeuf

For mostly historical reasons, the x86 oops dump shows the raw stack values:

...
[registers]

  Stack:
   ffff880079af7350 ffff880079905400 0000000000000000 ffffc900008f3ae0
   ffffffffa0196610 0000000000000001 00010000ffffffff 0000000087654321
   0000000000000002 0000000000000000 0000000000000000 0000000000000000
  Call Trace:
  ...

This seems to be an artifact from long ago, and probably isn't needed anymore. It generally just adds noise to the dump, and it can be actively harmful because it leaks kernel addresses.

Linus says:

"The stack dump actually goes back to forever, and it used to be
useful back in 1992 or so. But it used to be useful mainly because stacks were simpler and we didn't have very good call traces anyway. I definitely remember having used them - I just do not remember having used them in the last ten+ years.

Of course, it's still true that if you can trigger an oops, you've likely already lost the security game, but since the stack dump is so useless, let's aim to just remove it and make games like the above harder."

This also removes the related 'kstack=' cmdline option and the 'kstack_depth_to_print' sysctl.

Signed-off-by Josh Poimboeuf <[email protected]>

---
 Documentation/kernel-parameters.txt       |  3 --
 Documentation/sysctl/kernel.txt           |  8 -----
 Documentation/x86/x86_64/boot-options.txt |  4 ---
 arch/x86/include/asm/stacktrace.h         |  5 ---
 arch/x86/kernel/dumpstack.c               | 21 ++----------
 arch/x86/kernel/dumpstack_32.c            | 33 +------------------
 arch/x86/kernel/dumpstack_64.c            | 53 +------------------------------
 kernel/sysctl.c                           |  7 ----
 8 files changed, 4 insertions(+), 130 deletions(-)

Documentation/kernel-parameters.txt +0 -3

index 73de01e..def1874 100644
@@ -1952,9 +1952,6 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			kmemcheck=2 (one-shot mode)
 			Default: 2 (one-shot mode)
 
-	kstack=N	[X86] Print N words from the kernel stack
-			in oops dumps.
-
 	kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
 			Default is 0 (don't ignore, but inject #GP)

Documentation/sysctl/kernel.txt +0 -8

index ffab8b5..065f184 100644
@@ -40,7 +40,6 @@ show up in /proc/sys/kernel:
 - hung_task_warnings
 - kexec_load_disabled
 - kptr_restrict
-- kstack_depth_to_print       [ X86 only ]
 - l2cr                        [ PPC only ]
 - modprobe                    ==> Documentation/debugging-modules.txt
 - modules_disabled

@@ -395,13 +394,6 @@ When kptr_restrict is set to (2), kernel pointers printed using
 
 ==============================================================
 
-kstack_depth_to_print: (X86 only)
-
-Controls the number of words to print when dumping the raw
-kernel stack.
-
-==============================================================
-
 l2cr: (PPC only)
 
 This flag controls the L2 cache of G3 processor boards. If

Documentation/x86/x86_64/boot-options.txt +0 -4

index 0965a71..61b611e 100644
@@ -277,10 +277,6 @@ IOMMU (input/output memory management unit)
     space might stop working. Use this option if you have devices that
     are accessed from userspace directly on some PCI host bridge.
 
-Debugging
-
-  kstack=N	Print N words from the kernel stack in oops dumps.
-
 Miscellaneous
 
 	nogbpages

arch/x86/include/asm/stacktrace.h +0 -5

index 37f2e0b..1e375b0 100644
@@ -43,8 +43,6 @@ static inline bool on_stack(struct stack_info *info, void *addr, size_t len)
 		addr + len > begin && addr + len <= end);
 }
 
-extern int kstack_depth_to_print;
-
 #ifdef CONFIG_X86_32
 #define STACKSLOTS_PER_LINE 8
 #else

@@ -86,9 +84,6 @@ get_stack_pointer(struct task_struct *task, struct pt_regs *regs)
 void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
 			unsigned long *stack, char *log_lvl);
 
-void show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
-			unsigned long *sp, char *log_lvl);
-
 extern unsigned int code_bytes;
 
 /* The form of the top of the frame on the stack */

arch/x86/kernel/dumpstack.c +2 ~~-19~~

index f967652..499aa6f 100644
@@ -22,7 +22,6 @@
 int panic_on_unrecovered_nmi;
 int panic_on_io_nmi;
 unsigned int code_bytes = 64;
-int kstack_depth_to_print = 3 * STACKSLOTS_PER_LINE;
 static int die_counter;
 
 bool in_task_stack(unsigned long *stack, struct task_struct *task,

@@ -171,12 +170,12 @@ void show_stack(struct task_struct *task, unsigned long *sp)
 	if (!sp && task == current)
 		sp = get_stack_pointer(current, NULL);
 
-	show_stack_log_lvl(task, NULL, sp, KERN_DEFAULT);
+	show_trace_log_lvl(task, NULL, sp, KERN_DEFAULT);
 }
 
 void show_stack_regs(struct pt_regs *regs)
 {
-	show_stack_log_lvl(current, regs, NULL, KERN_DEFAULT);
+	show_trace_log_lvl(current, regs, NULL, KERN_DEFAULT);
 }
 
 static arch_spinlock_t die_lock = __ARCH_SPIN_LOCK_UNLOCKED;

@@ -295,22 +294,6 @@ void die(const char *str, struct pt_regs *regs, long err)
 	oops_end(flags, regs, sig);
 }
 
-static int __init kstack_setup(char *s)
-{
-	ssize_t ret;
-	unsigned long val;
-
-	if (!s)
-		return -EINVAL;
-
-	ret = kstrtoul(s, 0, &val);
-	if (ret)
-		return ret;
-	kstack_depth_to_print = val;
-	return 0;
-}
-early_param("kstack", kstack_setup);
-
 static int __init code_bytes_setup(char *s)
 {
 	ssize_t ret;

arch/x86/kernel/dumpstack_32.c +1 ~~-32~~

index 06eb322..90cf460 100644
@@ -121,36 +121,6 @@ int get_stack_info(unsigned long *stack, struct task_struct *task,
 	return -EINVAL;
 }
 
-void show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
-			unsigned long *sp, char *log_lvl)
-{
-	unsigned long *stack;
-	int i;
-
-	if (!try_get_task_stack(task))
-		return;
-
-	sp = sp ? : get_stack_pointer(task, regs);
-
-	stack = sp;
-	for (i = 0; i < kstack_depth_to_print; i++) {
-		if (kstack_end(stack))
-			break;
-		if ((i % STACKSLOTS_PER_LINE) == 0) {
-			if (i != 0)
-				pr_cont("\n");
-			printk("%s %08lx", log_lvl, *stack++);
-		} else
-			pr_cont(" %08lx", *stack++);
-		touch_nmi_watchdog();
-	}
-	pr_cont("\n");
-	show_trace_log_lvl(task, regs, sp, log_lvl);
-
-	put_task_stack(task);
-}
-
-
 void show_regs(struct pt_regs *regs)
 {
 	int i;

@@ -168,8 +138,7 @@ void show_regs(struct pt_regs *regs)
 		unsigned char c;
 		u8 *ip;
 
-		pr_emerg("Stack:\n");
-		show_stack_log_lvl(current, regs, NULL, KERN_EMERG);
+		show_trace_log_lvl(current, regs, NULL, KERN_EMERG);
 
 		pr_emerg("Code:");

arch/x86/kernel/dumpstack_64.c +1 ~~-52~~

65 lines not on this page · raw message

kernel/sysctl.c +0 -7

index 739fb17..39b3368 100644
@@ -983,13 +983,6 @@ static struct ctl_table kern_table[] = {
 		.proc_handler	= proc_dointvec,
 	},
 	{
-		.procname	= "kstack_depth_to_print",
-		.data		= &kstack_depth_to_print,
-		.maxlen		= sizeof(int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
-	},
-	{
 		.procname	= "io_delay_type",
 		.data		= &io_delay_type,
 		.maxlen		= sizeof(int),

Signature · 1 line

2.7.4

tip-bot for Josh Poimboeuf

merge bot

2016-10-26 05:43 UTC #14 lore raw

[tip:x86/asm] x86/dumpstack: Remove raw stack dump

x86/dumpstack: Remove raw stack dump

Commit-ID:  0ee1dd9f5e7eae4e55f95935b72d4beecb03de9c
Gitweb:     http://git.kernel.org/tip/0ee1dd9f5e7eae4e55f95935b72d4beecb03de9c
Author:     Josh Poimboeuf <[email protected]>
AuthorDate: Tue, 25 Oct 2016 09:51:13 -0500
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue, 25 Oct 2016 18:40:37 +0200

x86/dumpstack: Remove raw stack dump

For mostly historical reasons, the x86 oops dump shows the raw stack values:

...
[registers]

  Stack:
   ffff880079af7350 ffff880079905400 0000000000000000 ffffc900008f3ae0
   ffffffffa0196610 0000000000000001 00010000ffffffff 0000000087654321
   0000000000000002 0000000000000000 0000000000000000 0000000000000000
  Call Trace:
  ...

This seems to be an artifact from long ago, and probably isn't needed anymore. It generally just adds noise to the dump, and it can be actively harmful because it leaks kernel addresses.

Linus says:

This also removes the related 'kstack=' cmdline option and the 'kstack_depth_to_print' sysctl.

Signed-off-by Josh Poimboeuf <[email protected]>

Cc Andy Lutomirski <[email protected]>

Cc Borislav Petkov <[email protected]>

Cc Brian Gerst <[email protected]>

Cc Denys Vlasenko <[email protected]>

Cc H. Peter Anvin <[email protected]>

Cc Peter Zijlstra <[email protected]>

Cc Thomas Gleixner <[email protected]>

Link http://lkml.kernel.org/r/e83bd50df52d8fe88e94d2566426ae40d813bf8f.1477405374.git.jpoimboe@redhat.com open here

Signed-off-by Ingo Molnar <[email protected]>

---
 Documentation/kernel-parameters.txt       |  3 --
 Documentation/sysctl/kernel.txt           |  8 -----
 Documentation/x86/x86_64/boot-options.txt |  4 ---
 arch/x86/include/asm/stacktrace.h         |  5 ---
 arch/x86/kernel/dumpstack.c               | 21 ++----------
 arch/x86/kernel/dumpstack_32.c            | 33 +------------------
 arch/x86/kernel/dumpstack_64.c            | 53 +------------------------------
 kernel/sysctl.c                           |  7 ----
 8 files changed, 4 insertions(+), 130 deletions(-)

Documentation/kernel-parameters.txt +0 -3

index 37babf9..049a917 100644
@@ -1958,9 +1958,6 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			kmemcheck=2 (one-shot mode)
 			Default: 2 (one-shot mode)
 
-	kstack=N	[X86] Print N words from the kernel stack
-			in oops dumps.
-
 	kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
 			Default is 0 (don't ignore, but inject #GP)

Documentation/sysctl/kernel.txt +0 -8

index ffab8b5..065f184 100644
@@ -40,7 +40,6 @@ show up in /proc/sys/kernel:
 - hung_task_warnings
 - kexec_load_disabled
 - kptr_restrict
-- kstack_depth_to_print       [ X86 only ]
 - l2cr                        [ PPC only ]
 - modprobe                    ==> Documentation/debugging-modules.txt
 - modules_disabled

@@ -395,13 +394,6 @@ When kptr_restrict is set to (2), kernel pointers printed using
 
 ==============================================================
 
-kstack_depth_to_print: (X86 only)
-
-Controls the number of words to print when dumping the raw
-kernel stack.
-
-==============================================================
-
 l2cr: (PPC only)
 
 This flag controls the L2 cache of G3 processor boards. If

Documentation/x86/x86_64/boot-options.txt +0 -4

index 0965a71..61b611e 100644
@@ -277,10 +277,6 @@ IOMMU (input/output memory management unit)
     space might stop working. Use this option if you have devices that
     are accessed from userspace directly on some PCI host bridge.
 
-Debugging
-
-  kstack=N	Print N words from the kernel stack in oops dumps.
-
 Miscellaneous
 
 	nogbpages

arch/x86/include/asm/stacktrace.h +0 -5

index 37f2e0b..1e375b0 100644
@@ -43,8 +43,6 @@ static inline bool on_stack(struct stack_info *info, void *addr, size_t len)
 		addr + len > begin && addr + len <= end);
 }
 
-extern int kstack_depth_to_print;
-
 #ifdef CONFIG_X86_32
 #define STACKSLOTS_PER_LINE 8
 #else

@@ -86,9 +84,6 @@ get_stack_pointer(struct task_struct *task, struct pt_regs *regs)
 void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
 			unsigned long *stack, char *log_lvl);
 
-void show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
-			unsigned long *sp, char *log_lvl);
-
 extern unsigned int code_bytes;
 
 /* The form of the top of the frame on the stack */

arch/x86/kernel/dumpstack.c +2 ~~-19~~

index f967652..499aa6f 100644
@@ -22,7 +22,6 @@
 int panic_on_unrecovered_nmi;
 int panic_on_io_nmi;
 unsigned int code_bytes = 64;
-int kstack_depth_to_print = 3 * STACKSLOTS_PER_LINE;
 static int die_counter;
 
 bool in_task_stack(unsigned long *stack, struct task_struct *task,

@@ -171,12 +170,12 @@ void show_stack(struct task_struct *task, unsigned long *sp)
 	if (!sp && task == current)
 		sp = get_stack_pointer(current, NULL);
 
-	show_stack_log_lvl(task, NULL, sp, KERN_DEFAULT);
+	show_trace_log_lvl(task, NULL, sp, KERN_DEFAULT);
 }
 
 void show_stack_regs(struct pt_regs *regs)
 {
-	show_stack_log_lvl(current, regs, NULL, KERN_DEFAULT);
+	show_trace_log_lvl(current, regs, NULL, KERN_DEFAULT);
 }
 
 static arch_spinlock_t die_lock = __ARCH_SPIN_LOCK_UNLOCKED;

@@ -295,22 +294,6 @@ void die(const char *str, struct pt_regs *regs, long err)
 	oops_end(flags, regs, sig);
 }
 
-static int __init kstack_setup(char *s)
-{
-	ssize_t ret;
-	unsigned long val;
-
-	if (!s)
-		return -EINVAL;
-
-	ret = kstrtoul(s, 0, &val);
-	if (ret)
-		return ret;
-	kstack_depth_to_print = val;
-	return 0;
-}
-early_param("kstack", kstack_setup);
-
 static int __init code_bytes_setup(char *s)
 {
 	ssize_t ret;

arch/x86/kernel/dumpstack_32.c +1 ~~-32~~

index 06eb322..90cf460 100644
@@ -121,36 +121,6 @@ unknown:
 	return -EINVAL;
 }
 
-void show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
-			unsigned long *sp, char *log_lvl)
-{
-	unsigned long *stack;
-	int i;
-
-	if (!try_get_task_stack(task))
-		return;
-
-	sp = sp ? : get_stack_pointer(task, regs);
-
-	stack = sp;
-	for (i = 0; i < kstack_depth_to_print; i++) {
-		if (kstack_end(stack))
-			break;
-		if ((i % STACKSLOTS_PER_LINE) == 0) {
-			if (i != 0)
-				pr_cont("\n");
-			printk("%s %08lx", log_lvl, *stack++);
-		} else
-			pr_cont(" %08lx", *stack++);
-		touch_nmi_watchdog();
-	}
-	pr_cont("\n");
-	show_trace_log_lvl(task, regs, sp, log_lvl);
-
-	put_task_stack(task);
-}
-
-
 void show_regs(struct pt_regs *regs)
 {
 	int i;

@@ -168,8 +138,7 @@ void show_regs(struct pt_regs *regs)
 		unsigned char c;
 		u8 *ip;
 
-		pr_emerg("Stack:\n");
-		show_stack_log_lvl(current, regs, NULL, KERN_EMERG);
+		show_trace_log_lvl(current, regs, NULL, KERN_EMERG);
 
 		pr_emerg("Code:");

arch/x86/kernel/dumpstack_64.c +1 ~~-52~~

65 lines not on this page · raw message

kernel/sysctl.c +0 -7

index 706309f..17a5a82 100644
@@ -990,13 +990,6 @@ static struct ctl_table kern_table[] = {
 		.proc_handler	= proc_dointvec,
 	},
 	{
-		.procname	= "kstack_depth_to_print",
-		.data		= &kstack_depth_to_print,
-		.maxlen		= sizeof(int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
-	},
-	{
 		.procname	= "io_delay_type",
 		.data		= &io_delay_type,
 		.maxlen		= sizeof(int),

Josh Poimboeuf

author

2016-10-25 14:51 UTC #15 lore raw

PATCH 4/4 mm: remove kernel address exposure in free_reserved_area()

In reply to Josh Poimboeuf

Linus suggested we try to remove some of the low-hanging fruit related to kernel address exposure in dmesg. The only leaks I see on my local system are:

Freeing SMP alternatives memory: 32K (ffffffff9e309000 - ffffffff9e311000) Freeing initrd memory: 10588K (ffffa0b736b42000 - ffffa0b737599000) Freeing unused kernel memory: 3592K (ffffffff9df87000 - ffffffff9e309000) Freeing unused kernel memory: 1352K (ffffa0b7288ae000 - ffffa0b728a00000) Freeing unused kernel memory: 632K (ffffa0b728d62000 - ffffa0b728e00000)

Linus says:

"I suspect we should just remove [the addresses in the 'Freeing'
messages]. I'm sure they are useful in theory, but I suspect they were more useful back when the whole "free init memory" was originally done.

These days, if we have a use-after-free, I suspect the init-mem situation is the easiest situation by far. Compared to all the dynamic allocations which are much more likely to show it anyway. So having debug output for that case is likely not all that productive."

With this patch the freeing messages now look like this:

Freeing SMP alternatives memory: 32K
Freeing initrd memory: 10588K
Freeing unused kernel memory: 3592K
Freeing unused kernel memory: 1352K
Freeing unused kernel memory: 632K

Cc [email protected]

Signed-off-by Josh Poimboeuf <[email protected]>

---
 mm/page_alloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

mm/page_alloc.c +2 -2

index 2b3bf67..3f63973 100644
@@ -6508,8 +6508,8 @@ unsigned long free_reserved_area(void *start, void *end, int poison, char *s)
 	}
 
 	if (pages && s)
-		pr_info("Freeing %s memory: %ldK (%p - %p)\n",
-			s, pages << (PAGE_SHIFT - 10), start, end);
+		pr_info("Freeing %s memory: %ldK\n",
+			s, pages << (PAGE_SHIFT - 10));
 
 	return pages;
 }

Signature · 7 lines

2.7.4

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the body to [email protected].  For more info on Linux MM,
see: http://www.linux-mm.org/ .
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tip-bot for Josh Poimboeuf

merge bot

2016-10-26 05:43 UTC #16 lore raw

[tip:x86/asm] mm/page_alloc: Remove kernel address exposure in free_reserved_area()

mm/page_alloc: Remove kernel address exposure in free_reserved_area()

Commit-ID:  adb1fe9ae2ee6ef6bc10f3d5a588020e7664dfa7
Gitweb:     http://git.kernel.org/tip/adb1fe9ae2ee6ef6bc10f3d5a588020e7664dfa7
Author:     Josh Poimboeuf <[email protected]>
AuthorDate: Tue, 25 Oct 2016 09:51:14 -0500
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue, 25 Oct 2016 18:40:37 +0200

mm/page_alloc: Remove kernel address exposure in free_reserved_area()

Linus suggested we try to remove some of the low-hanging fruit related to kernel address exposure in dmesg. The only leaks I see on my local system are:

Linus says:

With this patch the freeing messages now look like this:

Freeing SMP alternatives memory: 32K
Freeing initrd memory: 10588K
Freeing unused kernel memory: 3592K
Freeing unused kernel memory: 1352K
Freeing unused kernel memory: 632K

Signed-off-by Josh Poimboeuf <[email protected]>

Cc Andy Lutomirski <[email protected]>

Cc Borislav Petkov <[email protected]>

Cc Brian Gerst <[email protected]>

Cc Denys Vlasenko <[email protected]>

Cc H. Peter Anvin <[email protected]>

Cc Peter Zijlstra <[email protected]>

Cc Thomas Gleixner <[email protected]>

Cc [email protected]

Link http://lkml.kernel.org/r/6836ff90c45b71d38e5d4405aec56fa9e5d1d4b2.1477405374.git.jpoimboe@redhat.com open here

Signed-off-by Ingo Molnar <[email protected]>

---
 mm/page_alloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

mm/page_alloc.c +2 -2

index 2b3bf67..3f63973 100644
@@ -6508,8 +6508,8 @@ unsigned long free_reserved_area(void *start, void *end, int poison, char *s)
 	}
 
 	if (pages && s)
-		pr_info("Freeing %s memory: %ldK (%p - %p)\n",
-			s, pages << (PAGE_SHIFT - 10), start, end);
+		pr_info("Freeing %s memory: %ldK\n",
+			s, pages << (PAGE_SHIFT - 10));
 
 	return pages;
 }