linux-kernel - [tip:x86/urgent] x86, smap: smap_violation() is bogus if CONFIG_X86

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Message-ID: <tip-f27d7759ad1ff48673831e598d6df4c76b2bcd06@git.kernel.org>
Date:	Thu, 13 Feb 2014 07:54:39 -0800
From:	"tip-bot for H. Peter Anvin" <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	tglx@...utronix.de, fengguang.wu@...el.com, hpa@...ux.intel.com
Subject: [tip:x86/urgent] x86, smap: smap_violation()
  is bogus if CONFIG_X86_SMAP is off

Commit-ID:  f27d7759ad1ff48673831e598d6df4c76b2bcd06
Gitweb:     http://git.kernel.org/tip/f27d7759ad1ff48673831e598d6df4c76b2bcd06
Author:     H. Peter Anvin <hpa@...ux.intel.com>
AuthorDate: Thu, 13 Feb 2014 07:46:04 -0800
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Thu, 13 Feb 2014 07:50:45 -0800

x86, smap: smap_violation() is bogus if CONFIG_X86_SMAP is off

If CONFIG_X86_SMAP is disabled, smap_violation() tests for conditions
which are incorrect (as the AC flag doesn't matter), causing spurious
faults.

The dynamic disabling of SMAP (nosmap on the command line) is fine
because it disables X86_FEATURE_SMAP, therefore causing the
static_cpu_has() to return false.

Found by Fengguang Wu's test system.

Reported-by: Fengguang Wu <fengguang.wu@...el.com>
Link: http://lkml.kernel.org/r/20140213124550.GA30497@localhost
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
Cc: <stable@...r.kernel.org> # v3.7+
---
 arch/x86/mm/fault.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 9d591c8..4b39bb7 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1087,12 +1087,14 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code)
 	if (unlikely(error_code & PF_RSVD))
 		pgtable_bad(regs, error_code, address);
 
+#ifdef CONFIG_X86_SMAP
 	if (static_cpu_has(X86_FEATURE_SMAP)) {
 		if (unlikely(smap_violation(error_code, regs))) {
 			bad_area_nosemaphore(regs, error_code, address);
 			return;
 		}
 	}
+#endif
 
 	/*
 	 * If we're in an interrupt, have no user context or are running
--
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