This is a note to let you know that I've just added the patch titled
KVM: VMX: Prevent RSB underflow before vmenter
to the 5.18-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:
kvm-vmx-prevent-rsb-underflow-before-vmenter.patch
and it can be found in the queue-5.18 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 Tue Jul 12 05:03:58 PM CEST 2022
From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Date: Tue, 14 Jun 2022 23:16:16 +0200
Subject: KVM: VMX: Prevent RSB underflow before vmenter
From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
commit 07853adc29a058c5fd143c14e5ac528448a72ed9 upstream.
On VMX, there are some balanced returns between the time the guest's
SPEC_CTRL value is written, and the vmenter.
Balanced returns (matched by a preceding call) are usually ok, but it's
at least theoretically possible an NMI with a deep call stack could
empty the RSB before one of the returns.
For maximum paranoia, don't allow *any* returns (balanced or otherwise)
between the SPEC_CTRL write and the vmenter.
[ bp: Fix 32-bit build. ]
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
[cascardo: header conflict fixup at arch/x86/kernel/asm-offsets.c]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/asm-offsets.c | 6 ++++++
arch/x86/kernel/cpu/bugs.c | 4 ++--
arch/x86/kvm/vmx/capabilities.h | 4 ++--
arch/x86/kvm/vmx/vmenter.S | 29 +++++++++++++++++++++++++++++
arch/x86/kvm/vmx/vmx.c | 8 --------
arch/x86/kvm/vmx/vmx.h | 4 ++--
arch/x86/kvm/vmx/vmx_ops.h | 2 +-
7 files changed, 42 insertions(+), 15 deletions(-)
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -18,6 +18,7 @@
#include <asm/bootparam.h>
#include <asm/suspend.h>
#include <asm/tlbflush.h>
+#include "../kvm/vmx/vmx.h"
#ifdef CONFIG_XEN
#include <xen/interface/xen.h>
@@ -90,4 +91,9 @@ static void __used common(void)
OFFSET(TSS_sp0, tss_struct, x86_tss.sp0);
OFFSET(TSS_sp1, tss_struct, x86_tss.sp1);
OFFSET(TSS_sp2, tss_struct, x86_tss.sp2);
+
+ if (IS_ENABLED(CONFIG_KVM_INTEL)) {
+ BLANK();
+ OFFSET(VMX_spec_ctrl, vcpu_vmx, spec_ctrl);
+ }
}
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -196,8 +196,8 @@ void __init check_bugs(void)
}
/*
- * NOTE: For VMX, this function is not called in the vmexit path.
- * It uses vmx_spec_ctrl_restore_host() instead.
+ * NOTE: This function is *only* called for SVM. VMX spec_ctrl handling is
+ * done in vmenter.S.
*/
void
x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -4,8 +4,8 @@
#include <asm/vmx.h>
-#include "lapic.h"
-#include "x86.h"
+#include "../lapic.h"
+#include "../x86.h"
extern bool __read_mostly enable_vpid;
extern bool __read_mostly flexpriority_enabled;
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -1,9 +1,11 @@
/* SPDX-License-Identifier: GPL-2.0 */
#include <linux/linkage.h>
#include <asm/asm.h>
+#include <asm/asm-offsets.h>
#include <asm/bitsperlong.h>
#include <asm/kvm_vcpu_regs.h>
#include <asm/nospec-branch.h>
+#include <asm/percpu.h>
#include <asm/segment.h>
#include "run_flags.h"
@@ -73,6 +75,33 @@ SYM_FUNC_START(__vmx_vcpu_run)
lea (%_ASM_SP), %_ASM_ARG2
call vmx_update_host_rsp
+ ALTERNATIVE "jmp .Lspec_ctrl_done", "", X86_FEATURE_MSR_SPEC_CTRL
+
+ /*
+ * SPEC_CTRL handling: if the guest's SPEC_CTRL value differs from the
+ * host's, write the MSR.
+ *
+ * IMPORTANT: To avoid RSB underflow attacks and any other nastiness,
+ * there must not be any returns or indirect branches between this code
+ * and vmentry.
+ */
+ mov 2*WORD_SIZE(%_ASM_SP), %_ASM_DI
+ movl VMX_spec_ctrl(%_ASM_DI), %edi
+ movl PER_CPU_VAR(x86_spec_ctrl_current), %esi
+ cmp %edi, %esi
+ je .Lspec_ctrl_done
+ mov $MSR_IA32_SPEC_CTRL, %ecx
+ xor %edx, %edx
+ mov %edi, %eax
+ wrmsr
+
+.Lspec_ctrl_done:
+
+ /*
+ * Since vmentry is serializing on affected CPUs, there's no need for
+ * an LFENCE to stop speculation from skipping the wrmsr.
+ */
+
/* Load @regs to RAX. */
mov (%_ASM_SP), %_ASM_AX
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6989,14 +6989,6 @@ static fastpath_t vmx_vcpu_run(struct kv
kvm_wait_lapic_expire(vcpu);
- /*
- * If this vCPU has touched SPEC_CTRL, restore the guest's value if
- * it's non-zero. Since vmentry is serialising on affected CPUs, there
- * is no need to worry about the conditional branch over the wrmsr
- * being speculatively taken.
- */
- x86_spec_ctrl_set_guest(vmx->spec_ctrl, 0);
-
/* The actual VMENTER/EXIT is in the .noinstr.text section. */
vmx_vcpu_enter_exit(vcpu, vmx, __vmx_vcpu_run_flags(vmx));
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -8,11 +8,11 @@
#include <asm/intel_pt.h>
#include "capabilities.h"
-#include "kvm_cache_regs.h"
+#include "../kvm_cache_regs.h"
#include "posted_intr.h"
#include "vmcs.h"
#include "vmx_ops.h"
-#include "cpuid.h"
+#include "../cpuid.h"
#include "run_flags.h"
#define MSR_TYPE_R 1
--- a/arch/x86/kvm/vmx/vmx_ops.h
+++ b/arch/x86/kvm/vmx/vmx_ops.h
@@ -8,7 +8,7 @@
#include "evmcs.h"
#include "vmcs.h"
-#include "x86.h"
+#include "../x86.h"
asmlinkage void vmread_error(unsigned long field, bool fault);
__attribute__((regparm(0))) void vmread_error_trampoline(unsigned long field,
Patches currently in stable-queue which might be from jpoimboe@xxxxxxxxxx are
queue-5.18/x86-sev-avoid-using-__x86_return_thunk.patch
queue-5.18/kvm-vmx-prevent-rsb-underflow-before-vmenter.patch
queue-5.18/x86-ftrace-use-alternative-ret-encoding.patch
queue-5.18/objtool-re-add-unwind_hint_-save_restore.patch
queue-5.18/x86-bugs-add-retbleed-ibpb.patch
queue-5.18/x86-retpoline-cleanup-some-ifdefery.patch
queue-5.18/kvm-vmx-flatten-__vmx_vcpu_run.patch
queue-5.18/x86-cpu-amd-add-spectral-chicken.patch
queue-5.18/kvm-vmx-fix-ibrs-handling-after-vmexit.patch
queue-5.18/kvm-vmx-prevent-guest-rsb-poisoning-attacks-with-eibrs.patch
queue-5.18/x86-vsyscall_emu-64-don-t-use-ret-in-vsyscall-emulation.patch
queue-5.18/objtool-skip-non-text-sections-when-adding-return-thunk-sites.patch
queue-5.18/x86-bugs-do-ibpb-fallback-check-only-once.patch
queue-5.18/x86-add-magic-amd-return-thunk.patch
queue-5.18/x86-bugs-keep-a-per-cpu-ia32_spec_ctrl-value.patch
queue-5.18/x86-objtool-create-.return_sites.patch
queue-5.18/x86-kvm-fix-setcc-emulation-for-return-thunks.patch
queue-5.18/x86-retpoline-swizzle-retpoline-thunk.patch
queue-5.18/x86-speculation-fix-firmware-entry-spec_ctrl-handling.patch
queue-5.18/x86-speculation-add-spectre_v2-ibrs-option-to-support-kernel-ibrs.patch
queue-5.18/x86-xen-add-untrain_ret.patch
queue-5.18/x86-undo-return-thunk-damage.patch
queue-5.18/x86-speculation-remove-x86_spec_ctrl_mask.patch
queue-5.18/x86-entry-avoid-very-early-ret.patch
queue-5.18/x86-speculation-fill-rsb-on-vmexit-for-ibrs.patch
queue-5.18/objtool-add-entry-unret-validation.patch
queue-5.18/kvm-vmx-convert-launched-argument-to-flags.patch
queue-5.18/x86-bpf-use-alternative-ret-encoding.patch
queue-5.18/x86-bugs-split-spectre_v2_select_mitigation-and-spectre_v2_user_select_mitigation.patch
queue-5.18/x86-bugs-report-intel-retbleed-vulnerability.patch
queue-5.18/x86-cpufeatures-move-retpoline-flags-to-word-11.patch
queue-5.18/x86-speculation-fix-spec_ctrl-write-on-smt-state-change.patch
queue-5.18/x86-retpoline-use-mfunction-return.patch
queue-5.18/x86-xen-rename-sys-entry-points.patch
queue-5.18/x86-bugs-optimize-spec_ctrl-msr-writes.patch
queue-5.18/x86-bugs-report-amd-retbleed-vulnerability.patch
queue-5.18/x86-static_call-use-alternative-ret-encoding.patch
queue-5.18/x86-speculation-fix-rsb-filling-with-config_retpoline-n.patch
queue-5.18/x86-use-return-thunk-in-asm-code.patch
queue-5.18/intel_idle-disable-ibrs-during-long-idle.patch
queue-5.18/x86-speculation-use-cached-host-spec_ctrl-value-for-guest-entry-exit.patch
queue-5.18/x86-bugs-add-amd-retbleed-boot-parameter.patch
queue-5.18/x86-entry-add-kernel-ibrs-implementation.patch
queue-5.18/objtool-treat-.text.__x86.-as-noinstr.patch
queue-5.18/objtool-update-retpoline-validation.patch
