[RFC PATCH 3/4] x86/traps: Attempt to fixup exceptions in vDSO before signaling

[Sean Christopherson]

Call fixup_vdso_exception() to attempt to fixup exceptions in vDSO code
before generating a signal for userspace faults.   This allows vDSO
functions to utilize exception fixup to report unhandled exceptions
directly to userspace for specific flows in lieu of generating a signal.

Suggested-by: Andy Lutomirski <l...@amacapital.net>
Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Jarkko Sakkinen <jarkko.sakki...@linux.intel.com>
Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: Josh Triplett <j...@joshtriplett.org>
Signed-off-by: Sean Christopherson <sean.j.christopher...@intel.com>
---
 arch/x86/kernel/traps.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 9b7c4ca8f0a7..106a6cc20ad6 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -61,6 +61,7 @@
 #include <asm/mpx.h>
 #include <asm/vm86.h>
 #include <asm/umip.h>
+#include <asm/vdso.h>
 
 #ifdef CONFIG_X86_64
 #include <asm/x86_init.h>
@@ -223,6 +224,10 @@ do_trap_no_signal(struct task_struct *tsk, int trapnr, 
const char *str,
        tsk->thread.error_code = error_code;
        tsk->thread.trap_nr = trapnr;
 
+       if (user_mode(regs) &&
+           fixup_vdso_exception(regs, trapnr, error_code, 0))
+               return 0;
+
        return -1;
 }
 
@@ -563,6 +568,9 @@ do_general_protection(struct pt_regs *regs, long error_code)
        tsk->thread.error_code = error_code;
        tsk->thread.trap_nr = X86_TRAP_GP;
 
+       if (fixup_vdso_exception(regs, X86_TRAP_GP, error_code, 0))
+               return;
+
        show_signal(tsk, SIGSEGV, "", desc, regs, error_code);
 
        force_sig(SIGSEGV, tsk);
@@ -854,6 +862,9 @@ static void math_error(struct pt_regs *regs, int 
error_code, int trapnr)
        if (!si_code)
                return;
 
+       if (fixup_vdso_exception(regs, trapnr, error_code, 0))
+               return;
+
        force_sig_fault(SIGFPE, si_code,
                        (void __user *)uprobe_get_trap_addr(regs), task);
 }
-- 
2.19.2