diff options
author | Josh Poimboeuf <jpoimboe@kernel.org> | 2022-06-14 23:16:13 +0200 |
---|---|---|
committer | Borislav Petkov <bp@suse.de> | 2022-06-27 10:34:00 +0200 |
commit | fc02735b14fff8c6678b521d324ade27b1a3d4cf (patch) | |
tree | 9be32b1a805858cab02c043a740b2bab8f45a15c /arch/x86/kvm/vmx/vmenter.S | |
parent | bb06650634d3552c0f8557e9d16aa1a408040e28 (diff) | |
download | linux-fc02735b14fff8c6678b521d324ade27b1a3d4cf.tar.bz2 |
KVM: VMX: Prevent guest RSB poisoning attacks with eIBRS
On eIBRS systems, the returns in the vmexit return path from
__vmx_vcpu_run() to vmx_vcpu_run() are exposed to RSB poisoning attacks.
Fix that by moving the post-vmexit spec_ctrl handling to immediately
after the vmexit.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Diffstat (limited to 'arch/x86/kvm/vmx/vmenter.S')
-rw-r--r-- | arch/x86/kvm/vmx/vmenter.S | 49 |
1 files changed, 38 insertions, 11 deletions
diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S index ddc3bf85db33..8641ea74a307 100644 --- a/arch/x86/kvm/vmx/vmenter.S +++ b/arch/x86/kvm/vmx/vmenter.S @@ -33,9 +33,10 @@ /** * __vmx_vcpu_run - Run a vCPU via a transition to VMX guest mode - * @vmx: struct vcpu_vmx * (forwarded to vmx_update_host_rsp) + * @vmx: struct vcpu_vmx * * @regs: unsigned long * (to guest registers) - * @flags: VMX_RUN_VMRESUME: use VMRESUME instead of VMLAUNCH + * @flags: VMX_RUN_VMRESUME: use VMRESUME instead of VMLAUNCH + * VMX_RUN_SAVE_SPEC_CTRL: save guest SPEC_CTRL into vmx->spec_ctrl * * Returns: * 0 on VM-Exit, 1 on VM-Fail @@ -54,6 +55,12 @@ SYM_FUNC_START(__vmx_vcpu_run) #endif push %_ASM_BX + /* Save @vmx for SPEC_CTRL handling */ + push %_ASM_ARG1 + + /* Save @flags for SPEC_CTRL handling */ + push %_ASM_ARG3 + /* * Save @regs, _ASM_ARG2 may be modified by vmx_update_host_rsp() and * @regs is needed after VM-Exit to save the guest's register values. @@ -149,25 +156,23 @@ SYM_INNER_LABEL(vmx_vmexit, SYM_L_GLOBAL) mov %r15, VCPU_R15(%_ASM_AX) #endif - /* IMPORTANT: RSB must be stuffed before the first return. */ - FILL_RETURN_BUFFER %_ASM_BX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE - - /* Clear RAX to indicate VM-Exit (as opposed to VM-Fail). */ - xor %eax, %eax + /* Clear return value to indicate VM-Exit (as opposed to VM-Fail). */ + xor %ebx, %ebx .Lclear_regs: /* - * Clear all general purpose registers except RSP and RAX to prevent + * Clear all general purpose registers except RSP and RBX to prevent * speculative use of the guest's values, even those that are reloaded * via the stack. In theory, an L1 cache miss when restoring registers * could lead to speculative execution with the guest's values. * Zeroing XORs are dirt cheap, i.e. the extra paranoia is essentially * free. RSP and RAX are exempt as RSP is restored by hardware during - * VM-Exit and RAX is explicitly loaded with 0 or 1 to return VM-Fail. + * VM-Exit and RBX is explicitly loaded with 0 or 1 to hold the return + * value. */ + xor %eax, %eax xor %ecx, %ecx xor %edx, %edx - xor %ebx, %ebx xor %ebp, %ebp xor %esi, %esi xor %edi, %edi @@ -185,6 +190,28 @@ SYM_INNER_LABEL(vmx_vmexit, SYM_L_GLOBAL) /* "POP" @regs. */ add $WORD_SIZE, %_ASM_SP + /* + * IMPORTANT: RSB filling and SPEC_CTRL handling must be done before + * the first unbalanced RET after vmexit! + * + * For retpoline, RSB filling is needed to prevent poisoned RSB entries + * and (in some cases) RSB underflow. + * + * eIBRS has its own protection against poisoned RSB, so it doesn't + * need the RSB filling sequence. But it does need to be enabled + * before the first unbalanced RET. + */ + + FILL_RETURN_BUFFER %_ASM_CX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE + + pop %_ASM_ARG2 /* @flags */ + pop %_ASM_ARG1 /* @vmx */ + + call vmx_spec_ctrl_restore_host + + /* Put return value in AX */ + mov %_ASM_BX, %_ASM_AX + pop %_ASM_BX #ifdef CONFIG_X86_64 pop %r12 @@ -204,7 +231,7 @@ SYM_INNER_LABEL(vmx_vmexit, SYM_L_GLOBAL) ud2 .Lvmfail: /* VM-Fail: set return value to 1 */ - mov $1, %eax + mov $1, %_ASM_BX jmp .Lclear_regs SYM_FUNC_END(__vmx_vcpu_run) |