From: Will Deacon will.deacon@arm.com
[ Upstream commit 88b0193d9418c00340e45e0a913a0813bc6c8c96 ]
Perf can generate and record a user callchain in response to a synchronous request, such as a tracepoint firing. If this happens under set_fs(KERNEL_DS), then we can end up walking the user stack (and dereferencing/saving whatever we find there) without the protections usually afforded by checks such as access_ok.
Rather than play whack-a-mole with each architecture's stack unwinding implementation, fix the root of the problem by ensuring that we force USER_DS when invoking perf_callchain_user from the perf core.
Reported-by: Al Viro viro@ZenIV.linux.org.uk Signed-off-by: Will Deacon will.deacon@arm.com Acked-by: Peter Zijlstra peterz@infradead.org Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Arnaldo Carvalho de Melo acme@redhat.com Cc: Jiri Olsa jolsa@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Thomas Gleixner tglx@linutronix.de Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- kernel/events/callchain.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c index e9fdb5203de5..411226b26bca 100644 --- a/kernel/events/callchain.c +++ b/kernel/events/callchain.c @@ -227,12 +227,18 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user, }
if (regs) { + mm_segment_t fs; + if (crosstask) goto exit_put;
if (add_mark) perf_callchain_store_context(&ctx, PERF_CONTEXT_USER); + + fs = get_fs(); + set_fs(USER_DS); perf_callchain_user(&ctx, regs); + set_fs(fs); } }