perf/core: Force USER_DS when recording user stack data

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 <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Cc: <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: 88b0193d9418 ("perf/callchain: Force USER_DS when invoking perf_callchain_user()")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index abaed4f8bb7f227bafdbc26b465df060a765eaf3..c80549bf82c6628fea20d230edc8b824e9f36f4d 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5943,6 +5943,7 @@ perf_output_sample_ustack(struct perf_output_handle *handle, u64 dump_size,
                unsigned long sp;
                unsigned int rem;
                u64 dyn_size;
+               mm_segment_t fs;
 
                /*
                 * We dump:
@@ -5960,7 +5961,10 @@ perf_output_sample_ustack(struct perf_output_handle *handle, u64 dump_size,
 
                /* 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);