x86, smap: A page fault due to SMAP is an oops

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

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1348256595-29119-11-git-send-email-hpa@linux.intel.com

1 files changed, 18 insertions, 0 deletions

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 76dcd9d8e0bc..f2fb75d46b96 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);
 
         /*