From: tip-bot for Andy Lutomirski <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: yu-cheng.yu@intel.com, dave.hansen@linux.intel.com,
brgerst@gmail.com, torvalds@linux-foundation.org,
mingo@kernel.org, peterz@infradead.org, bp@alien8.de,
tglx@linutronix.de, luto@amacapital.net, dvlasenk@redhat.com,
luto@kernel.org, riel@surriel.com, linux-kernel@vger.kernel.org,
hpa@zytor.com
Subject: [tip:x86/mm] x86/fault: Improve the condition for signalling vs OOPSing
Date: Tue, 20 Nov 2018 00:16:51 -0800 [thread overview]
Message-ID: <tip-6ea59b074f15e7ef4b042a108950861b383e7b02@git.kernel.org> (raw)
In-Reply-To: <10e509c43893170e262e82027ea399130ae81159.1542667307.git.luto@kernel.org>
Commit-ID: 6ea59b074f15e7ef4b042a108950861b383e7b02
Gitweb: https://git.kernel.org/tip/6ea59b074f15e7ef4b042a108950861b383e7b02
Author: Andy Lutomirski <luto@kernel.org>
AuthorDate: Mon, 19 Nov 2018 14:45:30 -0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 20 Nov 2018 08:44:29 +0100
x86/fault: Improve the condition for signalling vs OOPSing
__bad_area_nosemaphore() currently checks the X86_PF_USER bit in the
error code to decide whether to send a signal or to treat the fault
as a kernel error. This can cause somewhat erratic behavior. The
straightforward cases where the CPL agrees with the hardware USER
bit are all correct, but the other cases are confusing.
- A user instruction accessing a kernel address with supervisor
privilege (e.g. a descriptor table access failed). The USER bit
will be clear, and we OOPS. This is correct, because it indicates
a kernel bug, not a user error.
- A user instruction accessing a user address with supervisor
privilege (e.g. a descriptor table was incorrectly pointing at
user memory). __bad_area_nosemaphore() will be passed a modified
error code with the user bit set, and we will send a signal.
Sending the signal will work (because the regs and the entry
frame genuinely come from user mode), but we really ought to
OOPS, as this event indicates a severe kernel bug.
- A kernel instruction with user privilege (i.e. WRUSS). This
should OOPS or get fixed up. The current code would instead try
send a signal and malfunction.
Change the logic: a signal should be sent if the faulting context is
user mode *and* the access has user privilege. Otherwise it's
either a kernel mode fault or a failed implicit access, either of
which should end up in no_context().
Note to -stable maintainers: don't backport this unless you backport
CET. The bug it fixes is unobservable in current kernels unless
something is extremely wrong.
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/10e509c43893170e262e82027ea399130ae81159.1542667307.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/mm/fault.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 7a69b66cf071..3c9aed03d18e 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -794,7 +794,7 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
struct task_struct *tsk = current;
/* User mode accesses just cause a SIGSEGV */
- if (error_code & X86_PF_USER) {
+ if (user_mode(regs) && (error_code & X86_PF_USER)) {
/*
* It's possible to have interrupts off here:
*/
next prev parent reply other threads:[~2018-11-20 8:18 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:x86/mm] " tip-bot for Andy Lutomirski
2018-11-20 8:15 ` [PATCH 01/13] " 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-bot for Andy Lutomirski [this message]
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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