[PATCH 08/11] x86/fault: Bypass no_context() for implicit kernel faults from usermode

[Andy Lutomirski]

We can drop an indentation level and remove the last user_mode(regs) == true
caller of no_context() by directly OOPSing for implicit kernel faults from
usermode.

Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Andy Lutomirski <l...@kernel.org>
---
 arch/x86/mm/fault.c | 59 ++++++++++++++++++++++++---------------------
 1 file changed, 32 insertions(+), 27 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 6f43d080e1e8..177b612c7f33 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -789,44 +789,49 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned 
long error_code,
 {
        struct task_struct *tsk = current;
 
-       /* User mode accesses just cause a SIGSEGV */
-       if (user_mode(regs) && (error_code & X86_PF_USER)) {
-               /*
-                * It's possible to have interrupts off here:
-                */
-               local_irq_enable();
+       if (!user_mode(regs)) {
+               no_context(regs, error_code, address, pkey, si_code);
+               return;
+       }
 
-               /*
-                * Valid to do another page fault here because this one came
-                * from user space:
-                */
-               if (is_prefetch(regs, error_code, address))
-                       return;
+       if (!(error_code & X86_PF_USER)) {
+               /* Implicit user access to kernel memory -- just oops */
+               page_fault_oops(regs, error_code, address);
+               return;
+       }
 
-               if (is_errata100(regs, address))
-                       return;
+       /*
+        * User mode accesses just cause a SIGSEGV.
+        * It's possible to have interrupts off here:
+        */
+       local_irq_enable();
 
-               sanitize_error_code(address, &error_code);
+       /*
+        * Valid to do another page fault here because this one came
+        * from user space:
+        */
+       if (is_prefetch(regs, error_code, address))
+               return;
 
-               if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, 
address))
-                       return;
+       if (is_errata100(regs, address))
+               return;
 
-               if (likely(show_unhandled_signals))
-                       show_signal_msg(regs, error_code, address, tsk);
+       sanitize_error_code(address, &error_code);
 
-               set_signal_archinfo(address, error_code);
+       if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
+               return;
 
-               if (si_code == SEGV_PKUERR)
-                       force_sig_pkuerr((void __user *)address, pkey);
+       if (likely(show_unhandled_signals))
+               show_signal_msg(regs, error_code, address, tsk);
 
-               force_sig_fault(SIGSEGV, si_code, (void __user *)address);
+       set_signal_archinfo(address, error_code);
 
-               local_irq_disable();
+       if (si_code == SEGV_PKUERR)
+               force_sig_pkuerr((void __user *)address, pkey);
 
-               return;
-       }
+       force_sig_fault(SIGSEGV, si_code, (void __user *)address);
 
-       no_context(regs, error_code, address, SIGSEGV, si_code);
+       local_irq_disable();
 }
 
 static noinline void
-- 
2.29.2