[for-linus][PATCH 2/3] tracing: Fix check for trace_percpu_buffer validity in get_trace_buf()

[for-linus][PATCH 2/3] tracing: Fix check for trace_percpu_buffer validity in get_trace_buf()

[Steven Rostedt]

From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>

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.

Link: https://lkml.kernel.org/r/a920e4272e0b0635cf20c444707cbce1b2c8973d.1640255304.git.naveen.n.rao@linux.vnet.ibm.com

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

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 88de94da596b..e1f55851e53f 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -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++;
-- 
2.33.0

[for-linus][PATCH 3/3] tracing: Tag trace_percpu_buffer as a percpu pointer

[Steven Rostedt]

From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>

Tag trace_percpu_buffer as a percpu pointer to resolve warnings
reported by sparse:
  /linux/kernel/trace/trace.c:3218:46: warning: incorrect type in initializer (different address spaces)
  /linux/kernel/trace/trace.c:3218:46:    expected void const [noderef] __percpu *__vpp_verify
  /linux/kernel/trace/trace.c:3218:46:    got struct trace_buffer_struct *
  /linux/kernel/trace/trace.c:3234:9: warning: incorrect type in initializer (different address spaces)
  /linux/kernel/trace/trace.c:3234:9:    expected void const [noderef] __percpu *__vpp_verify
  /linux/kernel/trace/trace.c:3234:9:    got int *

Link: https://lkml.kernel.org/r/ebabd3f23101d89cb75671b68b6f819f5edc830b.1640255304.git.naveen.n.rao@linux.vnet.ibm.com

Cc: stable@vger.kernel.org
Reported-by: kernel test robot <lkp@intel.com>
Fixes: 07d777fe8c398 ("tracing: Add percpu buffers for trace_printk()")
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 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 e1f55851e53f..78ea542ce3bc 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
@@ -3236,7 +3236,7 @@ static void put_trace_buf(void)
 
 static int alloc_percpu_trace_buffer(void)
 {
-	struct trace_buffer_struct *buffers;
+	struct trace_buffer_struct __percpu *buffers;
 
 	if (trace_percpu_buffer)
 		return 0;
-- 
2.33.0