[PATCH v4 3/6] arm: KVM: Invalidate BTB on guest exit for Cortex-A12/A17
From: robin.murphy@arm.com (Robin Murphy)
Date: 2018-02-01 11:34:18
On 01/02/18 11:07, Marc Zyngier wrote:
quoted hunk ↗ jump to hunk
In order to avoid aliasing attacks against the branch predictor, let's invalidate the BTB on guest exit. This is made complicated by the fact that we cannot take a branch before invalidating the BTB. We only apply this to A12 and A17, which are the only two ARM cores on which this useful. Signed-off-by: Marc Zyngier <redacted> --- arch/arm/include/asm/kvm_asm.h | 2 -- arch/arm/include/asm/kvm_mmu.h | 18 ++++++++++- arch/arm/kvm/hyp/hyp-entry.S | 71 ++++++++++++++++++++++++++++++++++++++++-- 3 files changed, 86 insertions(+), 5 deletions(-)diff --git a/arch/arm/include/asm/kvm_asm.h b/arch/arm/include/asm/kvm_asm.h index 36dd2962a42d..df24ed48977d 100644 --- a/arch/arm/include/asm/kvm_asm.h +++ b/arch/arm/include/asm/kvm_asm.h@@ -61,8 +61,6 @@ struct kvm_vcpu; extern char __kvm_hyp_init[]; extern char __kvm_hyp_init_end[]; -extern char __kvm_hyp_vector[]; - extern void __kvm_flush_vm_context(void); extern void __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa); extern void __kvm_tlb_flush_vmid(struct kvm *kvm);diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h index a2d176a308bd..dedd4b8a3fa4 100644 --- a/arch/arm/include/asm/kvm_mmu.h +++ b/arch/arm/include/asm/kvm_mmu.h@@ -37,6 +37,7 @@ #include <linux/highmem.h> #include <asm/cacheflush.h> +#include <asm/cputype.h> #include <asm/pgalloc.h> #include <asm/stage2_pgtable.h>@@ -228,7 +229,22 @@ static inline unsigned int kvm_get_vmid_bits(void) static inline void *kvm_get_hyp_vector(void) { - return kvm_ksym_ref(__kvm_hyp_vector); + switch(read_cpuid_part()) { +#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR + case ARM_CPU_PART_CORTEX_A12: + case ARM_CPU_PART_CORTEX_A17: + { + extern char __kvm_hyp_vector_bp_inv[];
Super-nit: Is there a reason for scoping these declarations so tightly? Fair enough if there's something subtle I'm missing, but if not then it's probably a little more pleasant readability-wise to push them up a step into the function scope. Tangentially, I see there's already precedent so it's probably more of a general future KVM cleanup thing and doesn't need addressing in this context, but shouldn't these various code addresses strictly be const as well?
quoted hunk ↗ jump to hunk
+ return kvm_ksym_ref(__kvm_hyp_vector_bp_inv); + } + +#endif + default: + { + extern char __kvm_hyp_vector[]; + return kvm_ksym_ref(__kvm_hyp_vector); + } + } } static inline int kvm_map_vectors(void)diff --git a/arch/arm/kvm/hyp/hyp-entry.S b/arch/arm/kvm/hyp/hyp-entry.S index 95a2faefc070..e789f52a5129 100644 --- a/arch/arm/kvm/hyp/hyp-entry.S +++ b/arch/arm/kvm/hyp/hyp-entry.S@@ -71,6 +71,66 @@ __kvm_hyp_vector: W(b) hyp_irq W(b) hyp_fiq +#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR + .align 5 +__kvm_hyp_vector_bp_inv: + .global __kvm_hyp_vector_bp_inv + + /* + * We encode the exception entry in the bottom 3 bits of + * SP, and we have to guarantee to be 8 bytes aligned. + */ + W(add) sp, sp, #1 /* Reset 7 */ + W(add) sp, sp, #1 /* Undef 6 */ + W(add) sp, sp, #1 /* Syscall 5 */ + W(add) sp, sp, #1 /* Prefetch abort 4 */ + W(add) sp, sp, #1 /* Data abort 3 */ + W(add) sp, sp, #1 /* HVC 2 */ + W(add) sp, sp, #1 /* IRQ 1 */ + W(nop) /* FIQ 0 */ + + mcr p15, 0, r0, c7, c5, 6 /* BPIALL */ + isb + +#ifdef CONFIG_THUMB2_KERNEL + /* + * Yet another silly hack: Use VPIDR as a temp register. + * Thumb2 is really a pain, as SP cannot be used with most + * of the bitwise instructions. The vect_br macro ensures + * things gets cleaned-up. + */ + mcr p15, 4, r0, c0, c0, 0 /* VPIDR */ + mov r0, sp + and r0, r0, #7 + sub sp, sp, r0 + push {r1, r2} + mov r1, r0 + mrc p15, 4, r0, c0, c0, 0 /* VPIDR */ + mrc p15, 0, r2, c0, c0, 0 /* MIDR */ + mcr p15, 4, r2, c0, c0, 0 /* VPIDR */ +#endif + +.macro vect_br val, targ +ARM( eor sp, sp, #\val ) +ARM( tst sp, #7 ) +ARM( eorne sp, sp, #\val ) + +THUMB( cmp r1, #\val ) +THUMB( popeq {r1, r2} ) + + beq \targ +.endm + + vect_br 0, hyp_fiq + vect_br 1, hyp_irq + vect_br 2, hyp_hvc + vect_br 3, hyp_dabt + vect_br 4, hyp_pabt + vect_br 5, hyp_svc + vect_br 6, hyp_undef + vect_br 7, hyp_reset +#endif +
Otherwise, this now seems like it's about as nice as it's ever going to get (i.e. still not very...) Reviewed-by: Robin Murphy <robin.murphy@arm.com>
quoted hunk ↗ jump to hunk
.macro invalid_vector label, cause .align \label: mov r0, #\cause@@ -149,7 +209,14 @@ hyp_hvc: bx ip 1: - push {lr} + /* + * Pushing r2 here is just a way of keeping the stack aligned to + * 8 bytes on any path that can trigger a HYP exception. Here, + * we may well be about to jump into the guest, and the guest + * exit would otherwise be badly decoded by our fancy + * "decode-exception-without-a-branch" code... + */ + push {r2, lr} mov lr, r0 mov r0, r1@@ -159,7 +226,7 @@ hyp_hvc: THUMB( orr lr, #1) blx lr @ Call the HYP function - pop {lr} + pop {r2, lr} eret guest_trap: