This is a note to let you know that I've just added the patch titled
x86/speculation: Add LFENCE to RSB fill sequence
to the 4.14-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-speculation-add-lfence-to-rsb-fill-sequence.patch
and it can be found in the queue-4.14 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 Mon Oct 31 07:55:50 AM CET 2022
From: Suraj Jitindar Singh <surajjs@xxxxxxxxxx>
Date: Thu, 27 Oct 2022 13:55:11 -0700
Subject: x86/speculation: Add LFENCE to RSB fill sequence
To: <stable@xxxxxxxxxxxxxxx>
Cc: <surajjs@xxxxxxxxxx>, <sjitindarsingh@xxxxxxxxx>, <cascardo@xxxxxxxxxxxxx>, <kvm@xxxxxxxxxxxxxxx>, <pbonzini@xxxxxxxxxx>, <jpoimboe@xxxxxxxxxx>, <peterz@xxxxxxxxxxxxx>, <x86@xxxxxxxxxx>
Message-ID: <20221027205512.17684-3-surajjs@xxxxxxxxxx>
From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
commit ba6e31af2be96c4d0536f2152ed6f7b6c11bca47 upstream.
RSB fill sequence does not have any protection for miss-prediction of
conditional branch at the end of the sequence. CPU can speculatively
execute code immediately after the sequence, while RSB filling hasn't
completed yet.
#define __FILL_RETURN_BUFFER(reg, nr, sp) \
mov $(nr/2), reg; \
771: \
ANNOTATE_INTRA_FUNCTION_CALL; \
call 772f; \
773: /* speculation trap */ \
UNWIND_HINT_EMPTY; \
pause; \
lfence; \
jmp 773b; \
772: \
ANNOTATE_INTRA_FUNCTION_CALL; \
call 774f; \
775: /* speculation trap */ \
UNWIND_HINT_EMPTY; \
pause; \
lfence; \
jmp 775b; \
774: \
add $(BITS_PER_LONG/8) * 2, sp; \
dec reg; \
jnz 771b; <----- CPU can miss-predict here.
Before RSB is filled, RETs that come in program order after this macro
can be executed speculatively, making them vulnerable to RSB-based
attacks.
Mitigate it by adding an LFENCE after the conditional branch to prevent
speculation while RSB is being filled.
Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/nospec-branch.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -54,7 +54,9 @@
774: \
add $(BITS_PER_LONG/8) * 2, sp; \
dec reg; \
- jnz 771b;
+ jnz 771b; \
+ /* barrier for jnz misprediction */ \
+ lfence;
#ifdef __ASSEMBLY__
Patches currently in stable-queue which might be from surajjs@xxxxxxxxxx are
queue-4.14/x86-speculation-disable-rrsba-behavior.patch
queue-4.14/x86-bugs-report-intel-retbleed-vulnerability.patch
queue-4.14/x86-entry-add-kernel-ibrs-implementation.patch
queue-4.14/x86-bugs-warn-when-ibrs-mitigation-is-selected-on-enhanced-ibrs-parts.patch
queue-4.14/x86-cpu-add-a-steppings-field-to-struct-x86_cpu_id.patch
queue-4.14/x86-speculation-fix-spec_ctrl-write-on-smt-state-change.patch
queue-4.14/entel_idle-disable-ibrs-during-long-idle.patch
queue-4.14/x86-speculation-use-cached-host-spec_ctrl-value-for-guest-entry-exit.patch
queue-4.14/x86-speculation-change-fill_return_buffer-to-work-with-objtool.patch
queue-4.14/x86-speculation-add-lfence-to-rsb-fill-sequence.patch
queue-4.14/x86-bugs-report-amd-retbleed-vulnerability.patch
queue-4.14/x86-speculation-add-spectre_v2-ibrs-option-to-support-kernel-ibrs.patch
queue-4.14/x86-bugs-keep-a-per-cpu-ia32_spec_ctrl-value.patch
queue-4.14/x86-speculation-fill-rsb-on-vmexit-for-ibrs.patch
queue-4.14/x86-speculation-fix-rsb-filling-with-config_retpoline-n.patch
queue-4.14/x86-speculation-add-rsb-vm-exit-protections.patch
queue-4.14/x86-bugs-optimize-spec_ctrl-msr-writes.patch
queue-4.14/kvm-vmx-fix-ibrs-handling-after-vmexit.patch
queue-4.14/kvm-vmx-prevent-guest-rsb-poisoning-attacks-with-eibrs.patch
queue-4.14/x86-speculation-fix-firmware-entry-spec_ctrl-handling.patch
queue-4.14/x86-bugs-add-amd-retbleed-boot-parameter.patch
queue-4.14/x86-cpu-add-consistent-cpu-match-macros.patch
queue-4.14/x86-speculation-remove-x86_spec_ctrl_mask.patch
queue-4.14/x86-speculation-use-declare_per_cpu-for-x86_spec_ctrl_current.patch
queue-4.14/x86-cpufeature-fix-various-quality-problems-in-the-asm-cpu_device_hd.h-header.patch
queue-4.14/x86-entry-remove-skip_r11rcx.patch
queue-4.14/revert-x86-cpu-add-a-steppings-field-to-struct-x86_cpu_id.patch
queue-4.14/x86-common-stamp-out-the-stepping-madness.patch
queue-4.14/x86-cpu-amd-enumerate-btc_no.patch
queue-4.14/x86-bugs-add-cannon-lake-to-retbleed-affected-cpu-list.patch
queue-4.14/x86-devicetable-move-x86-specific-macro-out-of-generic-code.patch
queue-4.14/x86-bugs-split-spectre_v2_select_mitigation-and-spectre_v2_user_select_mitigation.patch
queue-4.14/x86-cpufeatures-move-retpoline-flags-to-word-11.patch
queue-4.14/x86-cpufeature-add-facility-to-check-for-min-microcode-revisions.patch
