tracing: Some more fixes for 6.0

Brian Norris (1):
tracefs: Only clobber mode/uid/gid on remount if asked

Christian A. Ehrhardt (1):
kprobes: Prohibit probes in gate area

----

 fs/tracefs/inode.c | 31 +++++++++++++++++++++++--------
 kernel/kprobes.c   |  1 +
 2 files changed, 24 insertions(+), 8 deletions(-)

From: "Christian A. Ehrhardt" <[email protected]>

The system call gate area counts as kernel text but trying to install a kprobe in this area fails with an Oops later on. To fix this explicitly disallow the gate area for kprobes.

Found by syzkaller with the following reproducer:
perf_event_open$cgroup(&(0x7f00000001c0)={0x6, 0x80, 0x0, 0x0, 0x0, 0x0, 0x80ffff, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, @perf_config_ext={0x0, 0xffffffffff600000}}, 0xffffffffffffffff, 0x0, 0xffffffffffffffff, 0x0)

Sample report:

BUG: unable to handle page fault for address: fffffbfff3ac6000
PGD 6dfcb067 P4D 6dfcb067 PUD 6df8f067 PMD 6de4d067 PTE 0
Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI
CPU: 0 PID: 21978 Comm: syz-executor.2 Not tainted 6.0.0-rc3-00363-g7726d4c3e60b-dirty #6
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
RIP: 0010:__insn_get_emulate_prefix arch/x86/lib/insn.c:91 [inline]
RIP: 0010:insn_get_emulate_prefix arch/x86/lib/insn.c:106 [inline]
RIP: 0010:insn_get_prefixes.part.0+0xa8/0x1110 arch/x86/lib/insn.c:134
Code: 49 be 00 00 00 00 00 fc ff df 48 8b 40 60 48 89 44 24 08 e9 81 00 00 00 e8 e5 4b 39 ff 4c 89 fa 4c 89 f9 48 c1 ea 03 83 e1 07 <42> 0f b6 14 32 38 ca 7f 08 84 d2 0f 85 06 10 00 00 48 89 d8 48 89
RSP: 0018:ffffc900088bf860 EFLAGS: 00010246
RAX: 0000000000040000 RBX: ffffffff9b9bebc0 RCX: 0000000000000000
RDX: 1ffffffff3ac6000 RSI: ffffc90002d82000 RDI: ffffc900088bf9e8
RBP: ffffffff9d630001 R08: 0000000000000000 R09: ffffc900088bf9e8
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000001
R13: ffffffff9d630000 R14: dffffc0000000000 R15: ffffffff9d630000
FS:  00007f63eef63640(0000) GS:ffff88806d000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffbfff3ac6000 CR3: 0000000029d90005 CR4: 0000000000770ef0
PKRU: 55555554
Call Trace:
 <TASK>
 insn_get_prefixes arch/x86/lib/insn.c:131 [inline]
 insn_get_opcode arch/x86/lib/insn.c:272 [inline]
 insn_get_modrm+0x64a/0x7b0 arch/x86/lib/insn.c:343
 insn_get_sib+0x29a/0x330 arch/x86/lib/insn.c:421
 insn_get_displacement+0x350/0x6b0 arch/x86/lib/insn.c:464
 insn_get_immediate arch/x86/lib/insn.c:632 [inline]
 insn_get_length arch/x86/lib/insn.c:707 [inline]
 insn_decode+0x43a/0x490 arch/x86/lib/insn.c:747
 can_probe+0xfc/0x1d0 arch/x86/kernel/kprobes/core.c:282
 arch_prepare_kprobe+0x79/0x1c0 arch/x86/kernel/kprobes/core.c:739
 prepare_kprobe kernel/kprobes.c:1160 [inline]
 register_kprobe kernel/kprobes.c:1641 [inline]
 register_kprobe+0xb6e/0x1690 kernel/kprobes.c:1603
 __register_trace_kprobe kernel/trace/trace_kprobe.c:509 [inline]
 __register_trace_kprobe+0x26a/0x2d0 kernel/trace/trace_kprobe.c:477
 create_local_trace_kprobe+0x1f7/0x350 kernel/trace/trace_kprobe.c:1833
 perf_kprobe_init+0x18c/0x280 kernel/trace/trace_event_perf.c:271
 perf_kprobe_event_init+0xf8/0x1c0 kernel/events/core.c:9888
 perf_try_init_event+0x12d/0x570 kernel/events/core.c:11261
 perf_init_event kernel/events/core.c:11325 [inline]
 perf_event_alloc.part.0+0xf7f/0x36a0 kernel/events/core.c:11619
 perf_event_alloc kernel/events/core.c:12059 [inline]
 __do_sys_perf_event_open+0x4a8/0x2a00 kernel/events/core.c:12157
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f63ef7efaed
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f63eef63028 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
RAX: ffffffffffffffda RBX: 00007f63ef90ff80 RCX: 00007f63ef7efaed
RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 00000000200001c0
RBP: 00007f63ef86019c R08: 0000000000000000 R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000002 R14: 00007f63ef90ff80 R15: 00007f63eef43000
 </TASK>
Modules linked in:
CR2: fffffbfff3ac6000
---[ end trace 0000000000000000 ]---
RIP: 0010:__insn_get_emulate_prefix arch/x86/lib/insn.c:91 [inline]
RIP: 0010:insn_get_emulate_prefix arch/x86/lib/insn.c:106 [inline]
RIP: 0010:insn_get_prefixes.part.0+0xa8/0x1110 arch/x86/lib/insn.c:134
Code: 49 be 00 00 00 00 00 fc ff df 48 8b 40 60 48 89 44 24 08 e9 81 00 00 00 e8 e5 4b 39 ff 4c 89 fa 4c 89 f9 48 c1 ea 03 83 e1 07 <42> 0f b6 14 32 38 ca 7f 08 84 d2 0f 85 06 10 00 00 48 89 d8 48 89
RSP: 0018:ffffc900088bf860 EFLAGS: 00010246
RAX: 0000000000040000 RBX: ffffffff9b9bebc0 RCX: 0000000000000000
RDX: 1ffffffff3ac6000 RSI: ffffc90002d82000 RDI: ffffc900088bf9e8
RBP: ffffffff9d630001 R08: 0000000000000000 R09: ffffc900088bf9e8
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000001
R13: ffffffff9d630000 R14: dffffc0000000000 R15: ffffffff9d630000
FS:  00007f63eef63640(0000) GS:ffff88806d000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffbfff3ac6000 CR3: 0000000029d90005 CR4: 0000000000770ef0

PKRU: 55555554
==================================================================

---
 kernel/kprobes.c | 1 +
 1 file changed, 1 insertion(+)

index 08350e35aba2..ca9d834d0b84 100644
@@ -1562,6 +1562,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
 	/* Ensure it is not in reserved area nor out of text */
 	if (!(core_kernel_text((unsigned long) p->addr) ||
 	    is_module_text_address((unsigned long) p->addr)) ||
+	    in_gate_area_no_mm((unsigned long) p->addr) ||
 	    within_kprobe_blacklist((unsigned long) p->addr) ||
 	    jump_label_text_reserved(p->addr, p->addr) ||
 	    static_call_text_reserved(p->addr, p->addr) ||

2.35.1

From: Brian Norris <[email protected]>

Users may have explicitly configured their tracefs permissions; we shouldn't overwrite those just because a second mount appeared.

Only clobber if the options were provided at mount time.

Note: the previous behavior was especially surprising in the presence of automounted /sys/kernel/debug/tracing/.

Existing behavior:

## Pre-existing status: tracefs is 0755.

  # stat -c '%A' /sys/kernel/tracing/
  drwxr-xr-x

## (Re)trigger the automount.

  # umount /sys/kernel/debug/tracing
  # stat -c '%A' /sys/kernel/debug/tracing/.
  drwx------

## Unexpected: the automount changed mode for other mount instances.

  # stat -c '%A' /sys/kernel/tracing/
  drwx------

New behavior (after this change):

## Pre-existing status: tracefs is 0755.

  # stat -c '%A' /sys/kernel/tracing/
  drwxr-xr-x

## (Re)trigger the automount.

  # umount /sys/kernel/debug/tracing
  # stat -c '%A' /sys/kernel/debug/tracing/.
  drwxr-xr-x

## Expected: the automount does not change other mount instances.

  # stat -c '%A' /sys/kernel/tracing/
  drwxr-xr-x

---
 fs/tracefs/inode.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

index 81d26abf486f..da85b3979195 100644
@@ -141,6 +141,8 @@ struct tracefs_mount_opts {
 	kuid_t uid;
 	kgid_t gid;
 	umode_t mode;
+	/* Opt_* bitfield. */
+	unsigned int opts;
 };
 
 enum {

@@ -241,6 +243,7 @@ static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
 	kgid_t gid;
 	char *p;
 
+	opts->opts = 0;
 	opts->mode = TRACEFS_DEFAULT_MODE;
 
 	while ((p = strsep(&data, ",")) != NULL) {

@@ -275,24 +278,36 @@ static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
 		 * but traditionally tracefs has ignored all mount options
 		 */
 		}
+
+		opts->opts |= BIT(token);
 	}
 
 	return 0;
 }
 
-static int tracefs_apply_options(struct super_block *sb)
+static int tracefs_apply_options(struct super_block *sb, bool remount)
 {
 	struct tracefs_fs_info *fsi = sb->s_fs_info;
 	struct inode *inode = d_inode(sb->s_root);
 	struct tracefs_mount_opts *opts = &fsi->mount_opts;
 
-	inode->i_mode &= ~S_IALLUGO;
-	inode->i_mode |= opts->mode;
+	/*
+	 * On remount, only reset mode/uid/gid if they were provided as mount
+	 * options.
+	 */
+
+	if (!remount || opts->opts & BIT(Opt_mode)) {
+		inode->i_mode &= ~S_IALLUGO;
+		inode->i_mode |= opts->mode;
+	}
 
-	inode->i_uid = opts->uid;
+	if (!remount || opts->opts & BIT(Opt_uid))
+		inode->i_uid = opts->uid;
 
-	/* Set all the group ids to the mount option */
-	set_gid(sb->s_root, opts->gid);
+	if (!remount || opts->opts & BIT(Opt_gid)) {
+		/* Set all the group ids to the mount option */
+		set_gid(sb->s_root, opts->gid);
+	}
 
 	return 0;
 }

@@ -307,7 +322,7 @@ static int tracefs_remount(struct super_block *sb, int *flags, char *data)
 	if (err)
 		goto fail;
 
-	tracefs_apply_options(sb);
+	tracefs_apply_options(sb, true);
 
 fail:
 	return err;

@@ -359,7 +374,7 @@ static int trace_fill_super(struct super_block *sb, void *data, int silent)
 
 	sb->s_op = &tracefs_super_operations;
 
-	tracefs_apply_options(sb);
+	tracefs_apply_options(sb, false);
 
 	return 0;
 

2.35.1