[PATCH 4.14 104/173] perf/core: Force USER_DS when recording user stack data

From: Greg Kroah-Hartman
Date: Mon Sep 24 2018 - 08:24:08 EST

4.14-stable review patch. If anyone has any objections, please let me know.


From: Yabin Cui <yabinc@xxxxxxxxxx>

commit 02e184476eff848273826c1d6617bb37e5bcc7ad upstream.

Perf can record user stack data in response to a synchronous request, such
as a tracepoint firing. If this happens under set_fs(KERNEL_DS), then we
end up reading user stack data using __copy_from_user_inatomic() under
set_fs(KERNEL_DS). I think this conflicts with the intention of using
set_fs(KERNEL_DS). And it is explicitly forbidden by hardware on ARM64
when both CONFIG_ARM64_UAO and CONFIG_ARM64_PAN are used.

So fix this by forcing USER_DS when recording user stack data.

Signed-off-by: Yabin Cui <yabinc@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: 88b0193d9418 ("perf/callchain: Force USER_DS when invoking perf_callchain_user()")
Link: http://lkml.kernel.org/r/20180823225935.27035-1-yabinc@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

kernel/events/core.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5700,6 +5700,7 @@ perf_output_sample_ustack(struct perf_ou
unsigned long sp;
unsigned int rem;
u64 dyn_size;
+ mm_segment_t fs;

* We dump:
@@ -5717,7 +5718,10 @@ perf_output_sample_ustack(struct perf_ou

/* Data. */
sp = perf_user_stack_pointer(regs);
+ fs = get_fs();
+ set_fs(USER_DS);
rem = __output_copy_user(handle, (void *) sp, dump_size);
+ set_fs(fs);
dyn_size = dump_size - rem;

perf_output_skip(handle, rem);