| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Fri, 27 Apr 2018 08:12:47 -0700
From: tip-bot for Andy Lutomirski <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: mingo@...nel.org, luto@...nel.org, hpa@...or.com, bp@...en8.de,
linux-kernel@...r.kernel.org, dvlasenk@...hat.com,
linux@...inikbrodowski.net, tglx@...utronix.de
Subject: [tip:x86/pti] x86/entry/64/compat: Preserve r8-r11 in int $0x80
Commit-ID: 8bb2610bc4967f19672444a7b0407367f1540028
Gitweb: https://git.kernel.org/tip/8bb2610bc4967f19672444a7b0407367f1540028
Author: Andy Lutomirski <luto@...nel.org>
AuthorDate: Tue, 17 Apr 2018 07:36:36 -0700
Committer: Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 27 Apr 2018 17:07:58 +0200
x86/entry/64/compat: Preserve r8-r11 in int $0x80
32-bit user code that uses int $80 doesn't care about r8-r11. There is,
however, some 64-bit user code that intentionally uses int $0x80 to invoke
32-bit system calls. From what I've seen, basically all such code assumes
that r8-r15 are all preserved, but the kernel clobbers r8-r11. Since I
doubt that there's any code that depends on int $0x80 zeroing r8-r11,
change the kernel to preserve them.
I suspect that very little user code is broken by the old clobber, since
r8-r11 are only rarely allocated by gcc, and they're clobbered by function
calls, so they only way we'd see a problem is if the same function that
invokes int $0x80 also spills something important to one of these
registers.
The current behavior seems to date back to the historical commit
"[PATCH] x86-64 merge for 2.6.4". Before that, all regs were
preserved. I can't find any explanation of why this change was made.
Update the test_syscall_vdso_32 testcase as well to verify the new
behavior, and it strengthens the test to make sure that the kernel doesn't
accidentally permute r8..r15.
Suggested-by: Denys Vlasenko <dvlasenk@...hat.com>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dominik Brodowski <linux@...inikbrodowski.net>
Link: https://lkml.kernel.org/r/d4c4d9985fbe64f8c9e19291886453914b48caee.1523975710.git.luto@kernel.org
---
arch/x86/entry/entry_64_compat.S | 8 +++---
tools/testing/selftests/x86/test_syscall_vdso.c | 35 +++++++++++++++----------
2 files changed, 25 insertions(+), 18 deletions(-)
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 9af927e59d49..9de7f1e1dede 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -84,13 +84,13 @@ ENTRY(entry_SYSENTER_compat)
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq $-ENOSYS /* pt_regs->ax */
- pushq $0 /* pt_regs->r8 = 0 */
+ pushq %r8 /* pt_regs->r8 */
xorl %r8d, %r8d /* nospec r8 */
- pushq $0 /* pt_regs->r9 = 0 */
+ pushq %r9 /* pt_regs->r9 */
xorl %r9d, %r9d /* nospec r9 */
- pushq $0 /* pt_regs->r10 = 0 */
+ pushq %r10 /* pt_regs->r10 */
xorl %r10d, %r10d /* nospec r10 */
- pushq $0 /* pt_regs->r11 = 0 */
+ pushq %r11 /* pt_regs->r11 */
xorl %r11d, %r11d /* nospec r11 */
pushq %rbx /* pt_regs->rbx */
xorl %ebx, %ebx /* nospec rbx */
diff --git a/tools/testing/selftests/x86/test_syscall_vdso.c b/tools/testing/selftests/x86/test_syscall_vdso.c
index 40370354d4c1..c9c3281077bc 100644
--- a/tools/testing/selftests/x86/test_syscall_vdso.c
+++ b/tools/testing/selftests/x86/test_syscall_vdso.c
@@ -100,12 +100,19 @@ asm (
" shl $32, %r8\n"
" orq $0x7f7f7f7f, %r8\n"
" movq %r8, %r9\n"
- " movq %r8, %r10\n"
- " movq %r8, %r11\n"
- " movq %r8, %r12\n"
- " movq %r8, %r13\n"
- " movq %r8, %r14\n"
- " movq %r8, %r15\n"
+ " incq %r9\n"
+ " movq %r9, %r10\n"
+ " incq %r10\n"
+ " movq %r10, %r11\n"
+ " incq %r11\n"
+ " movq %r11, %r12\n"
+ " incq %r12\n"
+ " movq %r12, %r13\n"
+ " incq %r13\n"
+ " movq %r13, %r14\n"
+ " incq %r14\n"
+ " movq %r14, %r15\n"
+ " incq %r15\n"
" ret\n"
" .code32\n"
" .popsection\n"
@@ -128,12 +135,13 @@ int check_regs64(void)
int err = 0;
int num = 8;
uint64_t *r64 = ®s64.r8;
+ uint64_t expected = 0x7f7f7f7f7f7f7f7fULL;
if (!kernel_is_64bit)
return 0;
do {
- if (*r64 == 0x7f7f7f7f7f7f7f7fULL)
+ if (*r64 == expected++)
continue; /* register did not change */
if (syscall_addr != (long)&int80) {
/*
@@ -147,18 +155,17 @@ int check_regs64(void)
continue;
}
} else {
- /* INT80 syscall entrypoint can be used by
+ /*
+ * INT80 syscall entrypoint can be used by
* 64-bit programs too, unlike SYSCALL/SYSENTER.
* Therefore it must preserve R12+
* (they are callee-saved registers in 64-bit C ABI).
*
- * This was probably historically not intended,
- * but R8..11 are clobbered (cleared to 0).
- * IOW: they are the only registers which aren't
- * preserved across INT80 syscall.
+ * Starting in Linux 4.17 (and any kernel that
+ * backports the change), R8..11 are preserved.
+ * Historically (and probably unintentionally), they
+ * were clobbered or zeroed.
*/
- if (*r64 == 0 && num <= 11)
- continue;
}
printf("[FAIL]\tR%d has changed:%016llx\n", num, *r64);
err++;
Powered by blists - more mailing lists