linux-kernel - [PATCH AUTOSEL 4.9 1/8] perf/core: Fix perf_sample_regs

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Message-Id: <20190703021847.18542-1-sashal@kernel.org>
Date:   Tue,  2 Jul 2019 22:18:40 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
        Young Xiao <92siuyang@...il.com>,
        Will Deacon <will.deacon@....com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Stephane Eranian <eranian@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.9 1/8] perf/core: Fix perf_sample_regs_user() mm check

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

[ Upstream commit 085ebfe937d7a7a5df1729f35a12d6d655fea68c ]

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>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7929526e96e2..93d7333c64d8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5492,7 +5492,7 @@ static void perf_sample_regs_user(struct perf_regs *regs_user,
 	if (user_mode(regs)) {
 		regs_user->abi = perf_reg_abi(current);
 		regs_user->regs = regs;
-	} else if (current->mm) {
+	} else if (!(current->flags & PF_KTHREAD)) {
 		perf_get_regs_user(regs_user, regs, regs_user_copy);
 	} else {
 		regs_user->abi = PERF_SAMPLE_REGS_ABI_NONE;
-- 
2.20.1