svn commit: r343780 - head/sys/amd64/amd64

[Konstantin Belousov]

Author: kib
Date: Tue Feb  5 17:49:27 2019
New Revision: 343780
URL: https://svnweb.freebsd.org/changeset/base/343780

Log:
  amd64: clear callee-preserved registers on syscall exit.
  
  %r8, %r10, and on non-KPTI configuration %r9 were not restored on fast
  return from a syscall.
  
  Reviewed by:	markj
  Approved by:	so
  Security:	CVE-2019-5595
  Sponsored by:	The FreeBSD Foundation
  MFC after:	0 minutes

Modified:
  head/sys/amd64/amd64/exception.S

Modified: head/sys/amd64/amd64/exception.S
==============================================================================
--- head/sys/amd64/amd64/exception.S	Tue Feb  5 17:17:12 2019	(r343779)
+++ head/sys/amd64/amd64/exception.S	Tue Feb  5 17:49:27 2019	(r343780)
@@ -521,12 +521,14 @@ fast_syscall_common:
 	movq	TF_RFLAGS(%rsp),%r11	/* original %rflags */
 	movq	TF_RIP(%rsp),%rcx	/* original %rip */
 	movq	TF_RSP(%rsp),%rsp	/* user stack pointer */
+	xorl	%r8d,%r8d		/* zero the rest of GPRs */
+	xorl	%r10d,%r10d
 	cmpq	$~0,PCPU(UCR3)
 	je	2f
 	movq	PCPU(UCR3),%r9
 	movq	%r9,%cr3
-	xorl	%r9d,%r9d
-2:	swapgs
+2:	xorl	%r9d,%r9d
+	swapgs
 	sysretq
 
 3:	/* AST scheduled. */