On Thu, Aug 23, 2018 at 03:59:35PM -0700, Yabin Cui wrote:
> 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
Ingo, I think this wants a stable tag too; seems to be a corrolary of:
88b0193d9418 ("perf/callchain: Force USER_DS when invoking
perf_callchain_user()")
Acked-by: Peter Zijlstra (Intel)
> ---
> kernel/events/core.c | 4
> 1 file changed, 4 insertions(+)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 2a62b96600ad..9bc047421e75 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5948,6 +5948,7 @@ 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:
> @@ -5965,7 +5966,10 @@ 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);
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
