git: c69096577383 - releng/13.0 - amd64: clear PSL.AC in the right frame

[Mark Johnston]

The branch releng/13.0 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=c690965773831b46f84a242b417372fc499302b4

commit c690965773831b46f84a242b417372fc499302b4
Author:     Konstantin Belousov <kib at FreeBSD.org>
AuthorDate: 2021-05-22 19:48:36 +0000
Commit:     Mark Johnston <markj at FreeBSD.org>
CommitDate: 2021-05-26 19:31:22 +0000

    amd64: clear PSL.AC in the right frame
    
    If copyin family of routines fault, kernel does clear PSL.AC on the
    fault entry, but the AC flag of the faulted frame is kept intact.  Since
    onfault handler is effectively jump, AC survives until syscall exit.
    
    Approved by:    so
    Security:       FreeBSD-SA-21:11.smap
    Security:       CVE-2021-29628
    Reported by:    m00nbsd, via Sony
    Reviewed by:    markj
    Sponsored by:   The FreeBSD Foundation
    admbugs:        975
    
    (cherry picked from commit 91aae953cb807d6fb7a70782b323bf9beb60d7c9)
    (cherry picked from commit 6bbde34ae6088285af9d1cc587249c3e7a0159a9)
---
 sys/amd64/amd64/support.S           | 18 ++++++++++++------
 sys/amd64/linux/linux_support.s     |  5 ++++-
 sys/amd64/linux32/linux32_support.s |  5 ++++-
 3 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/sys/amd64/amd64/support.S b/sys/amd64/amd64/support.S
index b623fba277db..7963071303b7 100644
--- a/sys/amd64/amd64/support.S
+++ b/sys/amd64/amd64/support.S
@@ -853,9 +853,11 @@ ENTRY(copyin_smap_erms)
 END(copyin_smap_erms)
 
 	ALIGN_TEXT
-	/* Trap entry clears PSL.AC */
 copy_fault:
-	movq	$0,PCB_ONFAULT(%r11)
+	testl	$CPUID_STDEXT_SMAP,cpu_stdext_feature(%rip)
+	je	1f
+	clac
+1:	movq	$0,PCB_ONFAULT(%r11)
 	movl	$EFAULT,%eax
 	POP_FRAME_POINTER
 	ret
@@ -1292,9 +1294,11 @@ ENTRY(subyte_smap)
 END(subyte_smap)
 
 	ALIGN_TEXT
-	/* Fault entry clears PSL.AC */
 fusufault:
-	movq	PCPU(CURPCB),%rcx
+	testl	$CPUID_STDEXT_SMAP,cpu_stdext_feature(%rip)
+	je	1f
+	clac
+1:	movq	PCPU(CURPCB),%rcx
 	xorl	%eax,%eax
 	movq	%rax,PCB_ONFAULT(%rcx)
 	decq	%rax
@@ -1377,8 +1381,10 @@ ENTRY(copyinstr_smap)
 END(copyinstr_smap)
 
 cpystrflt:
-	/* Fault entry clears PSL.AC */
-	movl	$EFAULT,%eax
+	testl	$CPUID_STDEXT_SMAP,cpu_stdext_feature(%rip)
+	je	1f
+	clac
+1:	movl	$EFAULT,%eax
 cpystrflt_x:
 	/* set *lencopied and return %eax */
 	movq	$0,PCB_ONFAULT(%r9)
diff --git a/sys/amd64/linux/linux_support.s b/sys/amd64/linux/linux_support.s
index 391f76414f22..2de778e151bf 100644
--- a/sys/amd64/linux/linux_support.s
+++ b/sys/amd64/linux/linux_support.s
@@ -34,7 +34,10 @@
 #include "assym.inc"
 
 futex_fault:
-	movq	$0,PCB_ONFAULT(%r8)
+	testl	$CPUID_STDEXT_SMAP,cpu_stdext_feature(%rip)
+	je	1f
+	clac
+1:	movq	$0,PCB_ONFAULT(%r8)
 	movl	$-EFAULT,%eax
 	ret
 
diff --git a/sys/amd64/linux32/linux32_support.s b/sys/amd64/linux32/linux32_support.s
index 981bba9f5821..7ff3e2293f6e 100644
--- a/sys/amd64/linux32/linux32_support.s
+++ b/sys/amd64/linux32/linux32_support.s
@@ -34,7 +34,10 @@
 #include "assym.inc"
 
 futex_fault:
-	movq	$0,PCB_ONFAULT(%r8)
+	testl	$CPUID_STDEXT_SMAP,cpu_stdext_feature(%rip)
+	je	1f
+	clac
+1:	movq	$0,PCB_ONFAULT(%r8)
 	movl	$-EFAULT,%eax
 	ret