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perf/callchain: Force USER_DS when invoking perf_callchain_user()

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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>
This commit is contained in:
Will Deacon 2017-05-09 18:00:04 +01:00 committed by Ingo Molnar
parent cefec66886
commit 88b0193d94
1 changed files with 6 additions and 0 deletions
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6
kernel/events/callchain.c
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@ -229,12 +229,18 @@ 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);
}
}