[RFC PATCH v3 3/4] x86/traps: Attempt to fixup exceptions in vDSO before signaling

[Sean Christopherson <sean.j.christopherson@intel.com>]

Call fixup_sgx_enclu_exception() in all trap flows that generate
signals to userspace immediately prior to generating any such signal.
If the exception is fixed, return cleanly and don't generate a signal.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kernel/traps.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 9b7c4ca8f0a7..dd664503803b 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/sgx.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_sgx_enclu_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_sgx_enclu_exception(regs, X86_TRAP_GP, error_code, 0))
+		return;
+
 	show_signal(tsk, SIGSEGV, "", desc, regs, error_code);
 
 	force_sig(SIGSEGV, tsk);
@@ -791,6 +799,10 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
 		goto exit;
 	}
 
+	if (user_mode(regs) &&
+	    fixup_sgx_enclu_exception(regs, X86_TRAP_DB, error_code, 0))
+		goto exit;
+
 	if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) {
 		/*
 		 * Historical junk that used to handle SYSENTER single-stepping.
@@ -854,6 +866,9 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
 	if (!si_code)
 		return;
 
+	if (fixup_sgx_enclu_exception(regs, trapnr, error_code, 0))
+		return;
+
 	force_sig_fault(SIGFPE, si_code,
 			(void __user *)uprobe_get_trap_addr(regs), task);
 }
-- 
2.19.2