| From foo@baz Mon Apr 9 17:09:24 CEST 2018 |
| From: Will Deacon <will.deacon@arm.com> |
| Date: Tue, 9 May 2017 18:00:04 +0100 |
| Subject: perf/callchain: Force USER_DS when invoking perf_callchain_user() |
| |
| 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> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| kernel/events/callchain.c | 6 ++++++ |
| 1 file changed, 6 insertions(+) |
| |
| --- a/kernel/events/callchain.c |
| +++ b/kernel/events/callchain.c |
| @@ -227,12 +227,18 @@ get_perf_callchain(struct pt_regs *regs, |
| } |
| |
| 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); |
| } |
| } |
| |
