This is a note to let you know that I've just added the patch titled
x86/syscall: Sanitize syscall table de-references under speculation fix
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-syscall-sanitize-syscall-table-de-references-under-speculation-fix.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From jslaby@xxxxxxx Wed Mar 7 07:05:55 2018
From: Jiri Slaby <jslaby@xxxxxxx>
Date: Wed, 7 Mar 2018 08:56:23 +0100
Subject: x86/syscall: Sanitize syscall table de-references under speculation fix
To: gregkh@xxxxxxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx, Jiri Slaby <jslaby@xxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Dan Williams <dan.j.williams@xxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, linux-arch@xxxxxxxxxxxxxxx, kernel-hardening@xxxxxxxxxxxxxxxxxx, Andy Lutomirski <luto@xxxxxxxxxx>, alan@xxxxxxxxxxxxxxx, Jinpu Wang <jinpu.wang@xxxxxxxxxxxxxxxx>
Message-ID: <20180307075623.12336-1-jslaby@xxxxxxx>
From: Jiri Slaby <jslaby@xxxxxxx>
In 4.4.118, we have commit c8961332d6da (x86/syscall: Sanitize syscall
table de-references under speculation), which is a backport of upstream
commit 2fbd7af5af86. But it fixed only the C part of the upstream patch
-- the IA32 sysentry. So it ommitted completely the assembly part -- the
64bit sysentry.
Fix that in this patch by explicit array_index_mask_nospec written in
assembly. The same was used in lib/getuser.S.
However, to have "sbb" working properly, we have to switch from "cmp"
against (NR_syscalls-1) to (NR_syscalls), otherwise the last syscall
number would be "and"ed by 0. It is because the original "ja" relies on
"CF" or "ZF", but we rely only on "CF" in "sbb". That means: switch to
"jae" conditional jump too.
Final note: use rcx for mask as this is exactly what is overwritten by
the 4th syscall argument (r10) right after.
Reported-by: Jan Beulich <JBeulich@xxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: kernel-hardening@xxxxxxxxxxxxxxxxxx
Cc: gregkh@xxxxxxxxxxxxxxxxxxx
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: alan@xxxxxxxxxxxxxxx
Cc: Jinpu Wang <jinpu.wang@xxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/entry/entry_64.S | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -178,12 +178,14 @@ GLOBAL(entry_SYSCALL_64_after_swapgs)
jnz tracesys
entry_SYSCALL_64_fastpath:
#if __SYSCALL_MASK == ~0
- cmpq $__NR_syscall_max, %rax
+ cmpq $NR_syscalls, %rax
#else
andl $__SYSCALL_MASK, %eax
- cmpl $__NR_syscall_max, %eax
+ cmpl $NR_syscalls, %eax
#endif
- ja 1f /* return -ENOSYS (already in pt_regs->ax) */
+ jae 1f /* return -ENOSYS (already in pt_regs->ax) */
+ sbb %rcx, %rcx /* array_index_mask_nospec() */
+ and %rcx, %rax
movq %r10, %rcx
#ifdef CONFIG_RETPOLINE
movq sys_call_table(, %rax, 8), %rax
@@ -276,12 +278,14 @@ tracesys_phase2:
RESTORE_C_REGS_EXCEPT_RAX
RESTORE_EXTRA_REGS
#if __SYSCALL_MASK == ~0
- cmpq $__NR_syscall_max, %rax
+ cmpq $NR_syscalls, %rax
#else
andl $__SYSCALL_MASK, %eax
- cmpl $__NR_syscall_max, %eax
+ cmpl $NR_syscalls, %eax
#endif
- ja 1f /* return -ENOSYS (already in pt_regs->ax) */
+ jae 1f /* return -ENOSYS (already in pt_regs->ax) */
+ sbb %rcx, %rcx /* array_index_mask_nospec() */
+ and %rcx, %rax
movq %r10, %rcx /* fixup for C */
#ifdef CONFIG_RETPOLINE
movq sys_call_table(, %rax, 8), %rax
Patches currently in stable-queue which might be from jslaby@xxxxxxx are
queue-4.4/x86-syscall-sanitize-syscall-table-de-references-under-speculation-fix.patch