[PATCH 4.9 39/43] KVM: arm64: Add templates for BHB mitigation sequences

Greg Kroah-Hartman
2022-04-06T20:04:05Z

From: James Morse <james.morse@arm.com>

KVM writes the Spectre-v2 mitigation template at the beginning of each
vector when a CPU requires a specific sequence to run.

Because the template is copied, it can not be modified by the alternatives
at runtime. As the KVM template code is intertwined with the bp-hardening
callbacks, all templates must have a bp-hardening callback.

Add templates for calling ARCH_WORKAROUND_3 and one for each value of K
in the brancy-loop. Identify these sequences by a new parameter
template_start, and add a copy of install_bp_hardening_cb() that is able to
install them.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm64/include/asm/cpucaps.h | 3 +
arch/arm64/include/asm/kvm_mmu.h | 2 -
arch/arm64/include/asm/mmu.h | 6 +++
arch/arm64/kernel/bpi.S | 50 +++++++++++++++++++++++++++
arch/arm64/kernel/cpu_errata.c | 71 +++++++++++++++++++++++++++++++++++++--
5 files changed, 128 insertions(+), 4 deletions(-)

--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -39,7 +39,8 @@
#define ARM64_SSBD 18
#define ARM64_MISMATCHED_CACHE_TYPE 19
#define ARM64_WORKAROUND_1188873 20
+#define ARM64_SPECTRE_BHB 21

-#define ARM64_NCAPS 21
+#define ARM64_NCAPS 22

#endif /* __ASM_CPUCAPS_H */
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -362,7 +362,7 @@ static inline void *kvm_get_hyp_vector(v
struct bp_hardening_data *data = arm64_get_bp_hardening_data();
void *vect = kvm_ksym_ref(__kvm_hyp_vector);

- if (data->fn) {
+ if (data->template_start) {
vect = __bp_harden_hyp_vecs_start +
data->hyp_vectors_slot * SZ_2K;

--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -45,6 +45,12 @@ typedef void (*bp_hardening_cb_t)(void);
struct bp_hardening_data {
int hyp_vectors_slot;
bp_hardening_cb_t fn;
+
+ /*
+ * template_start is only used by the BHB mitigation to identify the
+ * hyp_vectors_slot sequence.
+ */
+ const char *template_start;
};

#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
--- a/arch/arm64/kernel/bpi.S
+++ b/arch/arm64/kernel/bpi.S
@@ -73,3 +73,53 @@ ENTRY(__smccc_workaround_1_smc_end)
ENTRY(__smccc_workaround_1_hvc_start)
smccc_workaround_1 hvc
ENTRY(__smccc_workaround_1_hvc_end)
+
+ENTRY(__smccc_workaround_3_smc_start)
+ sub sp, sp, #(8 * 4)
+ stp x2, x3, [sp, #(8 * 0)]
+ stp x0, x1, [sp, #(8 * 2)]
+ mov w0, #ARM_SMCCC_ARCH_WORKAROUND_3
+ smc #0
+ ldp x2, x3, [sp, #(8 * 0)]
+ ldp x0, x1, [sp, #(8 * 2)]
+ add sp, sp, #(8 * 4)
+ENTRY(__smccc_workaround_3_smc_end)
+
+ENTRY(__spectre_bhb_loop_k8_start)
+ sub sp, sp, #(8 * 2)
+ stp x0, x1, [sp, #(8 * 0)]
+ mov x0, #8
+2: b . + 4
+ subs x0, x0, #1
+ b.ne 2b
+ dsb nsh
+ isb
+ ldp x0, x1, [sp, #(8 * 0)]
+ add sp, sp, #(8 * 2)
+ENTRY(__spectre_bhb_loop_k8_end)
+
+ENTRY(__spectre_bhb_loop_k24_start)
+ sub sp, sp, #(8 * 2)
+ stp x0, x1, [sp, #(8 * 0)]
+ mov x0, #24
+2: b . + 4
+ subs x0, x0, #1
+ b.ne 2b
+ dsb nsh
+ isb
+ ldp x0, x1, [sp, #(8 * 0)]
+ add sp, sp, #(8 * 2)
+ENTRY(__spectre_bhb_loop_k24_end)
+
+ENTRY(__spectre_bhb_loop_k32_start)
+ sub sp, sp, #(8 * 2)
+ stp x0, x1, [sp, #(8 * 0)]
+ mov x0, #32
+2: b . + 4
+ subs x0, x0, #1
+ b.ne 2b
+ dsb nsh
+ isb
+ ldp x0, x1, [sp, #(8 * 0)]
+ add sp, sp, #(8 * 2)
+ENTRY(__spectre_bhb_loop_k32_end)
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -74,6 +74,14 @@ extern char __smccc_workaround_1_smc_sta
extern char __smccc_workaround_1_smc_end[];
extern char __smccc_workaround_1_hvc_start[];
extern char __smccc_workaround_1_hvc_end[];
+extern char __smccc_workaround_3_smc_start[];
+extern char __smccc_workaround_3_smc_end[];
+extern char __spectre_bhb_loop_k8_start[];
+extern char __spectre_bhb_loop_k8_end[];
+extern char __spectre_bhb_loop_k24_start[];
+extern char __spectre_bhb_loop_k24_end[];
+extern char __spectre_bhb_loop_k32_start[];
+extern char __spectre_bhb_loop_k32_end[];

static void __copy_hyp_vect_bpi(int slot, const char *hyp_vecs_start,
const char *hyp_vecs_end)
@@ -87,12 +95,14 @@ static void __copy_hyp_vect_bpi(int slot
flush_icache_range((uintptr_t)dst, (uintptr_t)dst + SZ_2K);
}

+static DEFINE_SPINLOCK(bp_lock);
+static int last_slot = -1;
+
static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
const char *hyp_vecs_start,
const char *hyp_vecs_end)
{
- static int last_slot = -1;
- static DEFINE_SPINLOCK(bp_lock);
+
int cpu, slot = -1;

spin_lock(&bp_lock);
@@ -113,6 +123,7 @@ static void __install_bp_hardening_cb(bp

__this_cpu_write(bp_hardening_data.hyp_vectors_slot, slot);
__this_cpu_write(bp_hardening_data.fn, fn);
+ __this_cpu_write(bp_hardening_data.template_start, hyp_vecs_start);
spin_unlock(&bp_lock);
}
#else
@@ -544,3 +555,59 @@ const struct arm64_cpu_capabilities arm6
{
}
};
+
+#ifdef CONFIG_KVM
+static const char *kvm_bhb_get_vecs_end(const char *start)
+{
+ if (start == __smccc_workaround_3_smc_start)
+ return __smccc_workaround_3_smc_end;
+ else if (start == __spectre_bhb_loop_k8_start)
+ return __spectre_bhb_loop_k8_end;
+ else if (start == __spectre_bhb_loop_k24_start)
+ return __spectre_bhb_loop_k24_end;
+ else if (start == __spectre_bhb_loop_k32_start)
+ return __spectre_bhb_loop_k32_end;
+
+ return NULL;
+}
+
+void kvm_setup_bhb_slot(const char *hyp_vecs_start)
+{
+ int cpu, slot = -1;
+ const char *hyp_vecs_end;
+
+ if (!IS_ENABLED(CONFIG_KVM) || !is_hyp_mode_available())
+ return;
+
+ hyp_vecs_end = kvm_bhb_get_vecs_end(hyp_vecs_start);
+ if (WARN_ON_ONCE(!hyp_vecs_start || !hyp_vecs_end))
+ return;
+
+ spin_lock(&bp_lock);
+ for_each_possible_cpu(cpu) {
+ if (per_cpu(bp_hardening_data.template_start, cpu) == hyp_vecs_start) {
+ slot = per_cpu(bp_hardening_data.hyp_vectors_slot, cpu);
+ break;
+ }
+ }
+
+ if (slot == -1) {
+ last_slot++;
+ BUG_ON(((__bp_harden_hyp_vecs_end - __bp_harden_hyp_vecs_start)
+ / SZ_2K) <= last_slot);
+ slot = last_slot;
+ __copy_hyp_vect_bpi(slot, hyp_vecs_start, hyp_vecs_end);
+ }
+
+ __this_cpu_write(bp_hardening_data.hyp_vectors_slot, slot);
+ __this_cpu_write(bp_hardening_data.template_start, hyp_vecs_start);
+ spin_unlock(&bp_lock);
+}
+#else
+#define __smccc_workaround_3_smc_start NULL
+#define __spectre_bhb_loop_k8_start NULL
+#define __spectre_bhb_loop_k24_start NULL
+#define __spectre_bhb_loop_k32_start NULL
+
+void kvm_setup_bhb_slot(const char *hyp_vecs_start) { };
+#endif