This is a note to let you know that I've just added the patch titled
x86/entry/64: Clear registers for exceptions/interrupts, to reduce speculation attack surface
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-entry-64-clear-registers-for-exceptions-interrupts-to-reduce-speculation-attack-surface.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 3ac6d8c787b835b997eb23e43e09aa0895ef7d58 Mon Sep 17 00:00:00 2001
From: Dan Williams <dan.j.williams@xxxxxxxxx>
Date: Mon, 5 Feb 2018 17:18:11 -0800
Subject: x86/entry/64: Clear registers for exceptions/interrupts, to reduce speculation attack surface
From: Dan Williams <dan.j.williams@xxxxxxxxx>
commit 3ac6d8c787b835b997eb23e43e09aa0895ef7d58 upstream.
Clear the 'extra' registers on entering the 64-bit kernel for exceptions
and interrupts. The common registers are not cleared since they are
likely clobbered well before they can be exploited in a speculative
execution attack.
Originally-From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/151787989146.7847.15749181712358213254.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
[ Made small improvements to the changelog and the code comments. ]
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/entry/calling.h | 19 +++++++++++++++++++
arch/x86/entry/entry_64.S | 6 +++++-
2 files changed, 24 insertions(+), 1 deletion(-)
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -147,6 +147,25 @@ For 32-bit we have the following convent
UNWIND_HINT_REGS offset=\offset
.endm
+ /*
+ * Sanitize registers of values that a speculation attack
+ * might otherwise want to exploit. The lower registers are
+ * likely clobbered well before they could be put to use in
+ * a speculative execution gadget:
+ */
+ .macro CLEAR_REGS_NOSPEC
+ xorl %ebp, %ebp
+ xorl %ebx, %ebx
+ xorq %r8, %r8
+ xorq %r9, %r9
+ xorq %r10, %r10
+ xorq %r11, %r11
+ xorq %r12, %r12
+ xorq %r13, %r13
+ xorq %r14, %r14
+ xorq %r15, %r15
+ .endm
+
.macro POP_EXTRA_REGS
popq %r15
popq %r14
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -571,6 +571,7 @@ END(irq_entries_start)
ALLOC_PT_GPREGS_ON_STACK
SAVE_C_REGS
SAVE_EXTRA_REGS
+ CLEAR_REGS_NOSPEC
ENCODE_FRAME_POINTER
testb $3, CS(%rsp)
@@ -1127,6 +1128,7 @@ ENTRY(xen_failsafe_callback)
ALLOC_PT_GPREGS_ON_STACK
SAVE_C_REGS
SAVE_EXTRA_REGS
+ CLEAR_REGS_NOSPEC
ENCODE_FRAME_POINTER
jmp error_exit
END(xen_failsafe_callback)
@@ -1172,6 +1174,7 @@ ENTRY(paranoid_entry)
cld
SAVE_C_REGS 8
SAVE_EXTRA_REGS 8
+ CLEAR_REGS_NOSPEC
ENCODE_FRAME_POINTER 8
movl $1, %ebx
movl $MSR_GS_BASE, %ecx
@@ -1224,8 +1227,8 @@ ENTRY(error_entry)
cld
SAVE_C_REGS 8
SAVE_EXTRA_REGS 8
+ CLEAR_REGS_NOSPEC
ENCODE_FRAME_POINTER 8
- xorl %ebx, %ebx
testb $3, CS+8(%rsp)
jz .Lerror_kernelspace
@@ -1422,6 +1425,7 @@ ENTRY(nmi)
pushq %r14 /* pt_regs->r14 */
pushq %r15 /* pt_regs->r15 */
UNWIND_HINT_REGS
+ CLEAR_REGS_NOSPEC
ENCODE_FRAME_POINTER
/*
Patches currently in stable-queue which might be from dan.j.williams@xxxxxxxxx are
queue-4.14/x86-entry-64-interleave-xor-register-clearing-with-push-instructions.patch
queue-4.14/nospec-move-array_index_nospec-parameter-checking-into-separate-macro.patch
queue-4.14/x86-entry-64-merge-the-pop_c_regs-and-pop_extra_regs-macros-into-a-single-pop_regs-macro.patch
queue-4.14/kvm-nvmx-set-the-cpu_based_use_msr_bitmaps-if-we-have-a-valid-l02-msr-bitmap.patch
queue-4.14/x86-nvmx-properly-set-spec_ctrl-and-pred_cmd-before-merging-msrs.patch
queue-4.14/x86-speculation-add-asm-msr-index.h-dependency.patch
queue-4.14/x86-entry-64-use-push_and_clean_regs-in-more-cases.patch
queue-4.14/x86-speculation-update-speculation-control-microcode-blacklist.patch
queue-4.14/x86-entry-64-clear-registers-for-exceptions-interrupts-to-reduce-speculation-attack-surface.patch
queue-4.14/x86-speculation-correct-speculation-control-microcode-blacklist-again.patch
queue-4.14/x86-entry-64-merge-save_c_regs-and-save_extra_regs-remove-unused-extensions.patch
queue-4.14/x86-entry-64-indent-push_and_clear_regs-and-pop_regs-properly.patch
queue-4.14/x86-speculation-fix-up-array_index_nospec_mask-asm-constraint.patch
queue-4.14/x86-entry-64-clear-extra-registers-beyond-syscall-arguments-to-reduce-speculation-attack-surface.patch
queue-4.14/kvm-x86-reduce-retpoline-performance-impact-in-slot_handle_level_range-by-always-inlining-iterator-helper-methods.patch
queue-4.14/x86-mm-pti-fix-pti-comment-in-entry_syscall_64.patch
queue-4.14/x86-entry-64-get-rid-of-the-alloc_pt_gpregs_on_stack-and-save_and_clear_regs-macros.patch
queue-4.14/x86-speculation-clean-up-various-spectre-related-details.patch
queue-4.14/x86-entry-64-introduce-the-push_and_clean_regs-macro.patch
queue-4.14/revert-x86-speculation-simplify-indirect_branch_prediction_barrier.patch
queue-4.14/x86-entry-64-compat-clear-registers-for-compat-syscalls-to-reduce-speculation-attack-surface.patch
queue-4.14/x86-entry-64-fix-cr3-restore-in-paranoid_exit.patch