linux-kernel - [PATCH 3.16 66/87] perf/core: Fix perf_sample_regs

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Message-ID: <lsq.1570043211.918554389@decadent.org.uk>
Date:   Wed, 02 Oct 2019 20:06:51 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        "Arnaldo Carvalho de Melo" <acme@...hat.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...nel.org>,
        "Ravi Bangoria" <ravi.bangoria@...ux.vnet.ibm.com>,
        "Stephane Eranian" <eranian@...gle.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Young Xiao" <92siuyang@...il.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        "Jiri Olsa" <jolsa@...hat.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Will Deacon" <will.deacon@....com>,
        "Frederic Weisbecker" <fweisbec@...il.com>
Subject: [PATCH 3.16 66/87] perf/core: Fix perf_sample_regs_user() mm check

3.16.75-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@...radead.org>

commit 085ebfe937d7a7a5df1729f35a12d6d655fea68c upstream.

perf_sample_regs_user() uses 'current->mm' to test for the presence of
userspace, but this is insufficient, consider use_mm().

A better test is: '!(current->flags & PF_KTHREAD)', exec() clears
PF_KTHREAD after it sets the new ->mm but before it drops to userspace
for the first time.

Possibly obsoletes: bf05fc25f268 ("powerpc/perf: Fix oops when kthread execs user process")

Reported-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Reported-by: Young Xiao <92siuyang@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Will Deacon <will.deacon@....com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Fixes: 4018994f3d87 ("perf: Add ability to attach user level registers dump to sample")
Signed-off-by: Ingo Molnar <mingo@...nel.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4581,7 +4581,7 @@ static void perf_sample_regs_user(struct
 				  struct pt_regs *regs)
 {
 	if (!user_mode(regs)) {
-		if (current->mm)
+		if (!(current->flags & PF_KTHREAD))
 			regs = task_pt_regs(current);
 		else
 			regs = NULL;