linux-kernel - [PATCH 10/11] x86, smap: A page fault due to SMAP is an oops

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Message-Id: <1348256595-29119-11-git-send-email-hpa@linux.intel.com>
Date:	Fri, 21 Sep 2012 12:43:14 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linda Wang <lwang@...hat.com>,
	Matt Fleming <matt.fleming@...el.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: [PATCH 10/11] x86, smap: A page fault due to SMAP is an oops

From: "H. Peter Anvin" <hpa@...ux.intel.com>

If we get a page fault due to SMAP, trigger an oops rather than
spinning forever.

Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
---
 arch/x86/mm/fault.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 76dcd9d..f2fb75d 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -995,6 +995,17 @@ static int fault_in_kernel_space(unsigned long address)
 	return address >= TASK_SIZE_MAX;
 }
 
+static inline bool smap_violation(int error_code, struct pt_regs *regs)
+{
+	if (error_code & PF_USER)
+		return false;
+
+	if (!user_mode_vm(regs) && (regs->flags & X86_EFLAGS_AC))
+		return false;
+
+	return true;
+}
+
 /*
  * This routine handles page faults.  It determines the address,
  * and the problem, and then passes it off to one of the appropriate
@@ -1088,6 +1099,13 @@ do_page_fault(struct pt_regs *regs, unsigned long error_code)
 	if (unlikely(error_code & PF_RSVD))
 		pgtable_bad(regs, error_code, address);
 
+	if (static_cpu_has(X86_FEATURE_SMAP)) {
+		if (unlikely(smap_violation(error_code, regs))) {
+			bad_area_nosemaphore(regs, error_code, address);
+			return;
+		}
+	}
+
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
 
 	/*
-- 
1.7.6.5

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