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FAILED: patch "[PATCH] x86/dumpstack: Don't dump kernel memory based on usermode RIP" failed to apply to 4.18-stable tree

PATCH [email protected] 1 participant 1 message Sep 3, 2018

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Stable branch x86 x86 MM x86 stack unwinding
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The patch below does not apply to the 4.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

Quoted 1 line

From 342db04ae71273322f0011384a9ed414df8bdae4 Mon Sep 17 00:00:00 2001

From: Jann Horn <[email protected]>
Date: Tue, 28 Aug 2018 17:49:01 +0200
Subject: [PATCH] x86/dumpstack: Don't dump kernel memory based on usermode RIP

show_opcodes() is used both for dumping kernel instructions and for dumping user instructions. If userspace causes #PF by jumping to a kernel address, show_opcodes() can be reached with regs->ip controlled by the user, pointing to kernel code. Make sure that userspace can't trick us into dumping kernel memory into dmesg.

Fixes 7cccf0725cf7 ("x86/dumpstack: Add a show_ip() function")
Signed-off-by Jann Horn <[email protected]>
Signed-off-by Thomas Gleixner <[email protected]>
Reviewed-by Kees Cook <[email protected]>
Reviewed-by Borislav Petkov <[email protected]>
Cc "H. Peter Anvin" <[email protected]>
Cc Andy Lutomirski <[email protected]>
Cc [email protected]
Cc [email protected]
Link https://lkml.kernel.org/r/[email protected] open here
arch/x86/include/asm/stacktrace.h +1 -1
index b6dc698f992a..f335aad404a4 100644
@@ -111,6 +111,6 @@ static inline unsigned long caller_frame_pointer(void)
 	return (unsigned long)frame;
 }
 
-void show_opcodes(u8 *rip, const char *loglvl);
+void show_opcodes(struct pt_regs *regs, const char *loglvl);
 void show_ip(struct pt_regs *regs, const char *loglvl);
 #endif /* _ASM_X86_STACKTRACE_H */
arch/x86/kernel/dumpstack.c +13 -3
index 1596e6bfea6f..f56895106ccf 100644
@@ -90,14 +90,24 @@ static void printk_stack_address(unsigned long address, int reliable,
  * Thus, the 2/3rds prologue and 64 byte OPCODE_BUFSIZE is just a random
  * guesstimate in attempt to achieve all of the above.
  */
-void show_opcodes(u8 *rip, const char *loglvl)
+void show_opcodes(struct pt_regs *regs, const char *loglvl)
 {
 #define PROLOGUE_SIZE 42
 #define EPILOGUE_SIZE 21
 #define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE)
 	u8 opcodes[OPCODE_BUFSIZE];
+	unsigned long prologue = regs->ip - PROLOGUE_SIZE;
+	bool bad_ip;
 
-	if (probe_kernel_read(opcodes, rip - PROLOGUE_SIZE, OPCODE_BUFSIZE)) {
+	/*
+	 * Make sure userspace isn't trying to trick us into dumping kernel
+	 * memory by pointing the userspace instruction pointer at it.
+	 */
+	bad_ip = user_mode(regs) &&
+		__chk_range_not_ok(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX);
+
+	if (bad_ip || probe_kernel_read(opcodes, (u8 *)prologue,
+					OPCODE_BUFSIZE)) {
 		printk("%sCode: Bad RIP value.\n", loglvl);
 	} else {
 		printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"

@@ -113,7 +123,7 @@ void show_ip(struct pt_regs *regs, const char *loglvl)
 #else
 	printk("%sRIP: %04x:%pS\n", loglvl, (int)regs->cs, (void *)regs->ip);
 #endif
-	show_opcodes((u8 *)regs->ip, loglvl);
+	show_opcodes(regs, loglvl);
 }
 
 void show_iret_regs(struct pt_regs *regs)
arch/x86/mm/fault.c +1 -1
index b9123c497e0a..47bebfe6efa7 100644
@@ -837,7 +837,7 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
 
 	printk(KERN_CONT "\n");
 
-	show_opcodes((u8 *)regs->ip, loglvl);
+	show_opcodes(regs, loglvl);
 }
 
 static void