Re: [PATCH v3 1/3] arm64: errata: Assume that unknown CPUs _are_ vulnerable to Spectre BHB

Reviewed-by: Julius Werner jwerner@chromium.org

On Thu, Dec 19, 2024 at 9:54 PM Douglas Anderson dianders@chromium.org wrote:

The code for detecting CPUs that are vulnerable to Spectre BHB was based on a hardcoded list of CPU IDs that were known to be affected. Unfortunately, the list mostly only contained the IDs of standard ARM cores. The IDs for many cores that are minor variants of the standard ARM cores (like many Qualcomm Kyro CPUs) weren't listed. This led the code to assume that those variants were not affected.

Flip the code on its head and instead assume that a core is vulnerable if it doesn't have CSV2_3 but is unrecognized as being safe. This involves creating a "Spectre BHB safe" list.

As of right now, the only CPU IDs added to the "Spectre BHB safe" list are ARM Cortex A35, A53, A55, A510, and A520. This list was created by looking for cores that weren't listed in ARM's list [1] as per review feedback on v2 of this patch [2].

NOTE: this patch will not actually _mitigate_ anyone, it will simply cause them to report themselves as vulnerable. If any cores in the system are reported as vulnerable but not mitigated then the whole system will be reported as vulnerable though the system will attempt to mitigate with the information it has about the known cores.

[1] https://developer.arm.com/Arm%20Security%20Center/Spectre-BHB [2] https://lore.kernel.org/r/20241219175128.GA25477@willie-the-truck

Fixes: 558c303c9734 ("arm64: Mitigate spectre style branch history side channels") Cc: stable@vger.kernel.org Signed-off-by: Douglas Anderson dianders@chromium.org

---

Changes in v3:

• Don't guess the mitigation; just report unknown cores as vulnerable.
• Restructure the code since is_spectre_bhb_affected() defaults to true

Changes in v2:

• New

arch/arm64/include/asm/spectre.h | 1 - arch/arm64/kernel/proton-pack.c | 144 +++++++++++++++++-------------- 2 files changed, 77 insertions(+), 68 deletions(-)

diff --git a/arch/arm64/include/asm/spectre.h b/arch/arm64/include/asm/spectre.h index 0c4d9045c31f..f1524cdeacf1 100644 --- a/arch/arm64/include/asm/spectre.h +++ b/arch/arm64/include/asm/spectre.h @@ -97,7 +97,6 @@ enum mitigation_state arm64_get_meltdown_state(void);

enum mitigation_state arm64_get_spectre_bhb_state(void); bool is_spectre_bhb_affected(const struct arm64_cpu_capabilities *entry, int scope); -u8 spectre_bhb_loop_affected(int scope); void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *__unused); bool try_emulate_el1_ssbs(struct pt_regs *regs, u32 instr);

diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c index da53722f95d4..06e04c9e6480 100644 --- a/arch/arm64/kernel/proton-pack.c +++ b/arch/arm64/kernel/proton-pack.c @@ -845,52 +845,68 @@ static unsigned long system_bhb_mitigations;

• This must be called with SCOPE_LOCAL_CPU for each type of CPU, before any
• SCOPE_SYSTEM call will give the right answer.

*/ -u8 spectre_bhb_loop_affected(int scope) +static bool is_spectre_bhb_safe(int scope) +{

•   static const struct midr_range spectre_bhb_safe_list[] = {
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A35),
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A53),
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A55),
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A510),
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A520),
  

•           {},
  

•   };
  

•   static bool all_safe = true;
  

•   if (scope != SCOPE_LOCAL_CPU)
  

•           return all_safe;
  

•   if (is_midr_in_range_list(read_cpuid_id(), spectre_bhb_safe_list))
  

•           return true;
  

•   all_safe = false;
  

•   return false;
  

+}

+static u8 spectre_bhb_loop_affected(void) { u8 k = 0;

•   static u8 max_bhb_k;
  

•   if (scope == SCOPE_LOCAL_CPU) {
  

•           static const struct midr_range spectre_bhb_k32_list[] = {
  

•                   MIDR_ALL_VERSIONS(MIDR_CORTEX_A78),
  

•                   MIDR_ALL_VERSIONS(MIDR_CORTEX_A78AE),
  

•                   MIDR_ALL_VERSIONS(MIDR_CORTEX_A78C),
  

•                   MIDR_ALL_VERSIONS(MIDR_CORTEX_X1),
  

•                   MIDR_ALL_VERSIONS(MIDR_CORTEX_A710),
  

•                   MIDR_ALL_VERSIONS(MIDR_CORTEX_X2),
  

•                   MIDR_ALL_VERSIONS(MIDR_NEOVERSE_N2),
  

•                   MIDR_ALL_VERSIONS(MIDR_NEOVERSE_V1),
  

•                   {},
  

•           };
  

•           static const struct midr_range spectre_bhb_k24_list[] = {
  

•                   MIDR_ALL_VERSIONS(MIDR_CORTEX_A76),
  

•                   MIDR_ALL_VERSIONS(MIDR_CORTEX_A77),
  

•                   MIDR_ALL_VERSIONS(MIDR_NEOVERSE_N1),
  

•                   {},
  

•           };
  

•           static const struct midr_range spectre_bhb_k11_list[] = {
  

•                   MIDR_ALL_VERSIONS(MIDR_AMPERE1),
  

•                   {},
  

•           };
  

•           static const struct midr_range spectre_bhb_k8_list[] = {
  

•                   MIDR_ALL_VERSIONS(MIDR_CORTEX_A72),
  

•                   MIDR_ALL_VERSIONS(MIDR_CORTEX_A57),
  

•                   {},
  

•           };
  

•           if (is_midr_in_range_list(read_cpuid_id(), spectre_bhb_k32_list))
  

•                   k = 32;
  

•           else if (is_midr_in_range_list(read_cpuid_id(), spectre_bhb_k24_list))
  

•                   k = 24;
  

•           else if (is_midr_in_range_list(read_cpuid_id(), spectre_bhb_k11_list))
  

•                   k = 11;
  

•           else if (is_midr_in_range_list(read_cpuid_id(), spectre_bhb_k8_list))
  

•                   k =  8;
  

•           max_bhb_k = max(max_bhb_k, k);
  

•   } else {
  

•           k = max_bhb_k;
  

•   }
  

•   static const struct midr_range spectre_bhb_k32_list[] = {
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A78),
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A78AE),
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A78C),
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_X1),
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A710),
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_X2),
  

•           MIDR_ALL_VERSIONS(MIDR_NEOVERSE_N2),
  

•           MIDR_ALL_VERSIONS(MIDR_NEOVERSE_V1),
  

•           {},
  

•   };
  

•   static const struct midr_range spectre_bhb_k24_list[] = {
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A76),
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A77),
  

•           MIDR_ALL_VERSIONS(MIDR_NEOVERSE_N1),
  

•           {},
  

•   };
  

•   static const struct midr_range spectre_bhb_k11_list[] = {
  

•           MIDR_ALL_VERSIONS(MIDR_AMPERE1),
  

•           {},
  

•   };
  

•   static const struct midr_range spectre_bhb_k8_list[] = {
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A72),
  

•           MIDR_ALL_VERSIONS(MIDR_CORTEX_A57),
  

•           {},
  

•   };
  

•   if (is_midr_in_range_list(read_cpuid_id(), spectre_bhb_k32_list))
  

•           k = 32;
  

•   else if (is_midr_in_range_list(read_cpuid_id(), spectre_bhb_k24_list))
  

•           k = 24;
  

•   else if (is_midr_in_range_list(read_cpuid_id(), spectre_bhb_k11_list))
  

•           k = 11;
  

•   else if (is_midr_in_range_list(read_cpuid_id(), spectre_bhb_k8_list))
  

•           k =  8;
  
    return k;
  

} @@ -916,9 +932,8 @@ static enum mitigation_state spectre_bhb_get_cpu_fw_mitigation_state(void) } }

-static bool is_spectre_bhb_fw_affected(int scope) +static bool is_spectre_bhb_fw_affected(void) {

•   static bool system_affected;
    enum mitigation_state fw_state;
    bool has_smccc = arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_NONE;
    static const struct midr_range spectre_bhb_firmware_mitigated_list[] = {
  

@@ -929,16 +944,8 @@ static bool is_spectre_bhb_fw_affected(int scope) bool cpu_in_list = is_midr_in_range_list(read_cpuid_id(), spectre_bhb_firmware_mitigated_list);

•   if (scope != SCOPE_LOCAL_CPU)
  

•           return system_affected;
  

•   fw_state = spectre_bhb_get_cpu_fw_mitigation_state();
  

•   if (cpu_in_list || (has_smccc && fw_state == SPECTRE_MITIGATED)) {
  

•           system_affected = true;
  

•           return true;
  

•   }
  

•   return false;
  

•   return cpu_in_list || (has_smccc && fw_state == SPECTRE_MITIGATED);
  

}

static bool supports_ecbhb(int scope) @@ -954,6 +961,8 @@ static bool supports_ecbhb(int scope) ID_AA64MMFR1_EL1_ECBHB_SHIFT); }

+static u8 max_bhb_k;

bool is_spectre_bhb_affected(const struct arm64_cpu_capabilities *entry, int scope) { @@ -962,16 +971,18 @@ bool is_spectre_bhb_affected(const struct arm64_cpu_capabilities *entry, if (supports_csv2p3(scope)) return false;

•   if (supports_clearbhb(scope))
  

•           return true;
  

•   if (spectre_bhb_loop_affected(scope))
  

•           return true;
  

•   if (is_spectre_bhb_safe(scope))
  

•           return false;
  
  

•   if (is_spectre_bhb_fw_affected(scope))
  

•           return true;
  

•   /*
  

•    * At this point the core isn't known to be "safe" so we're going to
  

•    * assume it's vulnerable. We still need to update `max_bhb_k` though,
  

•    * but only if we aren't mitigating with clearbhb though.
  

•    */
  

•   if (scope == SCOPE_LOCAL_CPU && !supports_clearbhb(SCOPE_LOCAL_CPU))
  

•           max_bhb_k = max(max_bhb_k, spectre_bhb_loop_affected());
  
  

•   return false;
  

•   return true;
  

}

static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot) @@ -1028,7 +1039,7 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry) this_cpu_set_vectors(EL1_VECTOR_BHB_CLEAR_INSN); state = SPECTRE_MITIGATED; set_bit(BHB_INSN, &system_bhb_mitigations);

•   } else if (spectre_bhb_loop_affected(SCOPE_LOCAL_CPU)) {
  

•   } else if (spectre_bhb_loop_affected()) {
            /*
             * Ensure KVM uses the indirect vector which will have the
             * branchy-loop added. A57/A72-r0 will already have selected
  

@@ -1041,7 +1052,7 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry) this_cpu_set_vectors(EL1_VECTOR_BHB_LOOP); state = SPECTRE_MITIGATED; set_bit(BHB_LOOP, &system_bhb_mitigations);

•   } else if (is_spectre_bhb_fw_affected(SCOPE_LOCAL_CPU)) {
  

•   } else if (is_spectre_bhb_fw_affected()) {
            fw_state = spectre_bhb_get_cpu_fw_mitigation_state();
            if (fw_state == SPECTRE_MITIGATED) {
                    /*
  

@@ -1100,7 +1111,6 @@ void noinstr spectre_bhb_patch_loop_iter(struct alt_instr *alt, { u8 rd; u32 insn;

•   u16 loop_count = spectre_bhb_loop_affected(SCOPE_SYSTEM);
  
    BUG_ON(nr_inst != 1); /* MOV -> MOV */
  
  

@@ -1109,7 +1119,7 @@ void noinstr spectre_bhb_patch_loop_iter(struct alt_instr *alt,

    insn = le32_to_cpu(*origptr);
    rd = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RD, insn);

•   insn = aarch64_insn_gen_movewide(rd, loop_count, 0,
  

•   insn = aarch64_insn_gen_movewide(rd, max_bhb_k, 0,
                                     AARCH64_INSN_VARIANT_64BIT,
                                     AARCH64_INSN_MOVEWIDE_ZERO);
    *updptr++ = cpu_to_le32(insn);
  

-- 2.47.1.613.gc27f4b7a9f-goog