This is a note to let you know that I've just added the patch titled
arm64: use RET instruction for exiting the trampoline
to the 4.9-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:
arm64-use-ret-instruction-for-exiting-the-trampoline.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Thu Apr 5 21:39:28 CEST 2018
From: Mark Rutland <mark.rutland@xxxxxxx>
Date: Tue, 3 Apr 2018 12:09:11 +0100
Subject: arm64: use RET instruction for exiting the trampoline
To: stable@xxxxxxxxxxxxxxx
Cc: mark.brown@xxxxxxxxxx, ard.biesheuvel@xxxxxxxxxx, marc.zyngier@xxxxxxx, will.deacon@xxxxxxx
Message-ID: <20180403110923.43575-16-mark.rutland@xxxxxxx>
From: Will Deacon <will.deacon@xxxxxxx>
commit be04a6d1126b upstream.
Speculation attacks against the entry trampoline can potentially resteer
the speculative instruction stream through the indirect branch and into
arbitrary gadgets within the kernel.
This patch defends against these attacks by forcing a misprediction
through the return stack: a dummy BL instruction loads an entry into
the stack, so that the predicted program flow of the subsequent RET
instruction is to a branch-to-self instruction which is finally resolved
as a branch to the kernel vectors with speculation suppressed.
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxx> [v4.9 backport]
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> [v4.9 backport]
Tested-by: Will Deacon <will.deacon@xxxxxxx>
Tested-by: Greg Hackmann <ghackmann@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/kernel/entry.S | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -880,6 +880,14 @@ __ni_sys_trace:
.if \regsize == 64
msr tpidrro_el0, x30 // Restored in kernel_ventry
.endif
+ /*
+ * Defend against branch aliasing attacks by pushing a dummy
+ * entry onto the return stack and using a RET instruction to
+ * enter the full-fat kernel vectors.
+ */
+ bl 2f
+ b .
+2:
tramp_map_kernel x30
#ifdef CONFIG_RANDOMIZE_BASE
adr x30, tramp_vectors + PAGE_SIZE
@@ -892,7 +900,7 @@ __ni_sys_trace:
msr vbar_el1, x30
add x30, x30, #(1b - tramp_vectors)
isb
- br x30
+ ret
.endm
.macro tramp_exit, regsize = 64
Patches currently in stable-queue which might be from mark.rutland@xxxxxxx are
queue-4.9/arm64-mm-add-arm64_kernel_unmapped_at_el0-helper.patch
queue-4.9/arm64-entry-reword-comment-about-post_ttbr_update_workaround.patch
queue-4.9/arm64-kaslr-put-kernel-vectors-address-in-separate-data-page.patch
queue-4.9/arm64-turn-on-kpti-only-on-cpus-that-need-it.patch
queue-4.9/arm64-force-kpti-to-be-disabled-on-cavium-thunderx.patch
queue-4.9/arm64-mm-allocate-asids-in-pairs.patch
queue-4.9/arm64-tls-avoid-unconditional-zeroing-of-tpidrro_el0-for-native-tasks.patch
queue-4.9/arm64-use-ret-instruction-for-exiting-the-trampoline.patch
queue-4.9/arm64-entry-explicitly-pass-exception-level-to-kernel_ventry-macro.patch
queue-4.9/arm64-kpti-make-use-of-ng-dependent-on-arm64_kernel_unmapped_at_el0.patch
queue-4.9/arm64-mm-use-non-global-mappings-for-kernel-space.patch
queue-4.9/arm64-capabilities-handle-duplicate-entries-for-a-capability.patch
queue-4.9/arm64-entry-hook-up-entry-trampoline-to-exception-vectors.patch
queue-4.9/arm64-mm-invalidate-both-kernel-and-user-asids-when-performing-tlbi.patch
queue-4.9/arm64-mm-map-entry-trampoline-into-trampoline-and-kernel-page-tables.patch
queue-4.9/module-extend-rodata-off-boot-cmdline-parameter-to-module-mappings.patch
queue-4.9/arm64-kconfig-reword-unmap_kernel_at_el0-kconfig-entry.patch
queue-4.9/arm64-mm-move-asid-from-ttbr0-to-ttbr1.patch
queue-4.9/arm64-allow-checking-of-a-cpu-local-erratum.patch
queue-4.9/arm64-take-into-account-id_aa64pfr0_el1.csv3.patch
queue-4.9/arm64-kconfig-add-config_unmap_kernel_at_el0.patch
queue-4.9/arm64-idmap-use-awx-flags-for-.idmap.text-.pushsection-directives.patch
queue-4.9/arm64-factor-out-entry-stack-manipulation.patch
queue-4.9/arm64-entry-add-exception-trampoline-page-for-exceptions-from-el0.patch
queue-4.9/arm64-kpti-add-enable-callback-to-remap-swapper-using-ng-mappings.patch
queue-4.9/arm64-entry-add-fake-cpu-feature-for-unmapping-the-kernel-at-el0.patch
queue-4.9/arm64-cputype-add-midr-values-for-cavium-thunderx2-cpus.patch