From: tip-bot for Andy Lutomirski <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: luto@kernel.org, peterz@infradead.org,
linux-kernel@vger.kernel.org, mingo@kernel.org,
tglx@linutronix.de, hpa@zytor.com, bp@alien8.de,
luto@amacapital.net, yu-cheng.yu@intel.com, dvlasenk@redhat.com,
torvalds@linux-foundation.org, dave.hansen@linux.intel.com,
riel@surriel.com, brgerst@gmail.com
Subject: [tip:x86/mm] x86/fault: Check user_mode(regs) when avoiding an mmap_sem deadlock
Date: Tue, 20 Nov 2018 00:14:18 -0800 [thread overview]
Message-ID: <tip-6344be608c039f3a787f1144c46fcb04c0f76561@git.kernel.org> (raw)
In-Reply-To: <4b89b542e8ceba9bd6abde2f386afed6d99244a9.1542667307.git.luto@kernel.org>
Commit-ID: 6344be608c039f3a787f1144c46fcb04c0f76561
Gitweb: https://git.kernel.org/tip/6344be608c039f3a787f1144c46fcb04c0f76561
Author: Andy Lutomirski <luto@kernel.org>
AuthorDate: Mon, 19 Nov 2018 14:45:25 -0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 20 Nov 2018 08:44:27 +0100
x86/fault: Check user_mode(regs) when avoiding an mmap_sem deadlock
The fault-handling code that takes mmap_sem needs to avoid a
deadlock that could occur if the kernel took a bad (OOPS-worthy)
page fault on a user address while holding mmap_sem. This can only
happen if the faulting instruction was in the kernel
(i.e. user_mode(regs)). Rather than checking the sw_error_code
(which will have the USER bit set if the fault was a USER-permission
access *or* if user_mode(regs)), just check user_mode(regs)
directly.
The old code would have malfunctioned if the kernel executed a bogus
WRUSS instruction while holding mmap_sem. Fortunately, that is
extremely unlikely in current kernels, which don't use WRUSS.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/4b89b542e8ceba9bd6abde2f386afed6d99244a9.1542667307.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/mm/fault.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 29525cf21100..8624cb7d8d65 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1344,13 +1344,10 @@ void do_user_addr_fault(struct pt_regs *regs,
* Only do the expensive exception table search when we might be at
* risk of a deadlock. This happens if we
* 1. Failed to acquire mmap_sem, and
- * 2. The access did not originate in userspace. Note: either the
- * hardware or earlier page fault code may set X86_PF_USER
- * in sw_error_code.
+ * 2. The access did not originate in userspace.
*/
if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
- if (!(sw_error_code & X86_PF_USER) &&
- !search_exception_tables(regs->ip)) {
+ if (!user_mode(regs) && !search_exception_tables(regs->ip)) {
/*
* Fault from code in kernel from
* which we do not expect faults.
next prev parent reply other threads:[~2018-11-20 8:16 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-19 22:45 [PATCH 00/13] x86/fault: #PF improvements, mostly related to USER bit Andy Lutomirski
2018-11-19 22:45 ` [PATCH 01/13] x86/fault: Check user_mode(regs) when avoiding an mmap_sem deadlock Andy Lutomirski
2018-11-20 8:14 ` tip-bot for Andy Lutomirski [this message]
2018-11-20 8:15 ` Peter Zijlstra
2018-11-19 22:45 ` [PATCH 02/13] x86/fault: Check user_mode(regs) when validating a stack extension Andy Lutomirski
2018-11-20 7:39 ` Ingo Molnar
2018-11-20 8:13 ` Ingo Molnar
2018-11-19 22:45 ` [PATCH 03/13] x86/cpufeatures, x86/fault: Mark SMAP as disabled when configured out Andy Lutomirski
2018-11-20 8:15 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 04/13] x86/fault: Fold smap_violation() into do_user_addr_fault() Andy Lutomirski
2018-11-20 8:15 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 05/13] x86/fault: Fix SMAP #PF handling buglet for implicit supervisor accesses Andy Lutomirski
2018-11-20 8:16 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 06/13] x86/fault: Improve the condition for signalling vs OOPSing Andy Lutomirski
2018-11-20 8:16 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 07/13] x86/fault: Make error_code sanitization more robust Andy Lutomirski
2018-11-20 8:17 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 08/13] x86/fault: Don't set thread.cr2, etc before OOPSing Andy Lutomirski
2018-11-20 8:17 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2018-11-19 22:45 ` [PATCH 09/13] x86/fault: Remove sw_error_code Andy Lutomirski
2018-11-19 22:45 ` [PATCH 10/13] x86/fault: Don't try to recover from an implicit supervisor access Andy Lutomirski
2018-11-19 22:45 ` [PATCH 11/13] x86/oops: Show the correct CS value in show_regs() Andy Lutomirski
2018-11-19 22:45 ` [PATCH 12/13] x86/fault: Decode page fault OOPSes better Andy Lutomirski
2018-11-27 14:46 ` Sean Christopherson
2018-11-19 22:45 ` [PATCH 13/13] x86/vsyscall/64: Use X86_PF constants in the simulated #PF error code Andy Lutomirski
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