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Subject[PATCH] trace: Fix check for trace_percpu_buffer validity in get_trace_buf()
Date
With the new osnoise tracer, we are seeing the below splat:
Kernel attempted to read user page (c7d880000) - exploit attempt? (uid: 0)
BUG: Unable to handle kernel data access on read at 0xc7d880000
Faulting instruction address: 0xc0000000002ffa10
Oops: Kernel access of bad area, sig: 11 [#1]
LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
...
NIP [c0000000002ffa10] __trace_array_vprintk.part.0+0x70/0x2f0
LR [c0000000002ff9fc] __trace_array_vprintk.part.0+0x5c/0x2f0
Call Trace:
[c0000008bdd73b80] [c0000000001c49cc] put_prev_task_fair+0x3c/0x60 (unreliable)
[c0000008bdd73be0] [c000000000301430] trace_array_printk_buf+0x70/0x90
[c0000008bdd73c00] [c0000000003178b0] trace_sched_switch_callback+0x250/0x290
[c0000008bdd73c90] [c000000000e70d60] __schedule+0x410/0x710
[c0000008bdd73d40] [c000000000e710c0] schedule+0x60/0x130
[c0000008bdd73d70] [c000000000030614] interrupt_exit_user_prepare_main+0x264/0x270
[c0000008bdd73de0] [c000000000030a70] syscall_exit_prepare+0x150/0x180
[c0000008bdd73e10] [c00000000000c174] system_call_vectored_common+0xf4/0x278

osnoise tracer on ppc64le is triggering osnoise_taint() for negative
duration in get_int_safe_duration() called from
trace_sched_switch_callback()->thread_exit().

The problem though is that the check for a valid trace_percpu_buffer is
incorrect in get_trace_buf(). The check is being done after calculating
the pointer for the current cpu, rather than on the main percpu pointer.
Fix the check to be against trace_percpu_buffer. Also tag
trace_percpu_buffer as a percpu pointer.

Fixes: e2ace001176dc9 ("tracing: Choose static tp_printk buffer by explicit nesting count")
Cc: stable@vger.kernel.org
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
kernel/trace/trace.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 88de94da596b13..6a8bf33c413c99 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3207,7 +3207,7 @@ struct trace_buffer_struct {
char buffer[4][TRACE_BUF_SIZE];
};

-static struct trace_buffer_struct *trace_percpu_buffer;
+static struct trace_buffer_struct __percpu *trace_percpu_buffer;

/*
* This allows for lockless recording. If we're nested too deeply, then
@@ -3217,7 +3217,7 @@ static char *get_trace_buf(void)
{
struct trace_buffer_struct *buffer = this_cpu_ptr(trace_percpu_buffer);

- if (!buffer || buffer->nesting >= 4)
+ if (!trace_percpu_buffer || buffer->nesting >= 4)
return NULL;

buffer->nesting++;
base-commit: f7f0bb5eaecb1aff9cc8ab13425d43690b71ec44
--
2.34.1

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