x86/fault: Don't try to recover from an implicit supervisor access

This avoids a situation in which we attempt to apply various fixups
that are not intended to handle implicit supervisor accesses from
user mode if we screw up in a way that causes this type of fault.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.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/9999f151d72ff352265f3274c5ab3a4105090f49.1542841400.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 82881bc..ca38bd0 100644 (file)
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -653,6 +653,15 @@ no_context(struct pt_regs *regs, unsigned long error_code,
        unsigned long flags;
        int sig;
 
+       if (user_mode(regs)) {
+               /*
+                * This is an implicit supervisor-mode access from user
+                * mode.  Bypass all the kernel-mode recovery code and just
+                * OOPS.
+                */
+               goto oops;
+       }
+
        /* Are we prepared to handle this kernel fault? */
        if (fixup_exception(regs, X86_TRAP_PF, error_code, address)) {
                /*
@@ -738,6 +747,7 @@ no_context(struct pt_regs *regs, unsigned long error_code,
        if (IS_ENABLED(CONFIG_EFI))
                efi_recover_from_page_fault(address);
 
+oops:
        /*
         * Oops. The kernel tried to access some bad page. We'll have to
         * terminate things with extreme prejudice: