svn commit: r343789 - releng/11.2/sys/amd64/amd64

[Ed Maste]

Author: emaste
Date: Tue Feb  5 18:07:45 2019
New Revision: 343789
URL: https://svnweb.freebsd.org/changeset/base/343789

Log:
  amd64: clear callee-preserved registers on syscall exit
  
  Submitted by:	kib
  Approved by:	so
  Security:	CVE-2019-5595
  Security:	FreeBSD-SA-19:01.syscall

Modified:
  releng/11.2/sys/amd64/amd64/exception.S

Modified: releng/11.2/sys/amd64/amd64/exception.S
==============================================================================
--- releng/11.2/sys/amd64/amd64/exception.S	Tue Feb  5 18:05:05 2019	(r343788)
+++ releng/11.2/sys/amd64/amd64/exception.S	Tue Feb  5 18:07:45 2019	(r343789)
@@ -496,12 +496,14 @@ 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
 	cmpb	$0,pti
 	je	2f
 	movq	PCPU(UCR3),%r9
 	movq	%r9,%cr3
-	xorl	%r9d,%r9d
-2:	swapgs
+2:	xorl	%r9d,%r9d
+	swapgs
 	sysretq
 
 3:	/* AST scheduled. */