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xen
6227866a-Arm-Spectre-BHB-handling.patch
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File 6227866a-Arm-Spectre-BHB-handling.patch of Package xen
# Commit 62c91eb66a2904eefb1d1d9642e3697a1e3c3a3c # Date 2022-03-08 16:38:02 +0000 # Author Rahul Singh <rahul.singh@arm.com> # Committer Andrew Cooper <andrew.cooper3@citrix.com> xen/arm: Add Spectre BHB handling This commit is adding Spectre BHB handling to Xen on Arm. The commit is introducing new alternative code to be executed during exception entry: - SMCC workaround 3 call - loop workaround (with 8, 24 or 32 iterations) - use of new clearbhb instruction Cpuerrata is modified by this patch to apply the required workaround for CPU affected by Spectre BHB when CONFIG_ARM64_HARDEN_BRANCH_PREDICTOR is enabled. To do this the system previously used to apply smcc workaround 1 is reused and new alternative code to be copied in the exception handler is introduced. To define the type of workaround required by a processor, 4 new cpu capabilities are introduced (for each number of loop and for smcc workaround 3). When a processor is affected, enable_spectre_bhb_workaround is called and if the processor does not have CSV2 set to 3 or ECBHB feature (which would mean that the processor is doing what is required in hardware), the proper code is enabled at exception entry. In the case where workaround 3 is not supported by the firmware, we enable workaround 1 when possible as it will also mitigate Spectre BHB on systems without CSV2. This is part of XSA-398 / CVE-2022-23960. Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com> Signed-off-by: Rahul Singh <rahul.singh@arm.com> Acked-by: Julien Grall <julien@xen.org> --- a/xen/arch/arm/arm64/bpi.S +++ b/xen/arch/arm/arm64/bpi.S @@ -58,16 +58,42 @@ ENTRY(__bp_harden_hyp_vecs_start) .endr ENTRY(__bp_harden_hyp_vecs_end) -ENTRY(__smccc_workaround_1_smc_start) +.macro mitigate_spectre_bhb_loop count +ENTRY(__mitigate_spectre_bhb_loop_start_\count) + stp x0, x1, [sp, #-16]! + mov x0, \count +.Lspectre_bhb_loop\@: + b . + 4 + subs x0, x0, #1 + b.ne .Lspectre_bhb_loop\@ + sb + ldp x0, x1, [sp], #16 +ENTRY(__mitigate_spectre_bhb_loop_end_\count) +.endm + +.macro smccc_workaround num smcc_id +ENTRY(__smccc_workaround_smc_start_\num) sub sp, sp, #(8 * 4) stp x0, x1, [sp, #(8 * 2)] stp x2, x3, [sp, #(8 * 0)] - mov w0, #ARM_SMCCC_ARCH_WORKAROUND_1_FID + mov w0, \smcc_id smc #0 ldp x2, x3, [sp, #(8 * 0)] ldp x0, x1, [sp, #(8 * 2)] add sp, sp, #(8 * 4) -ENTRY(__smccc_workaround_1_smc_end) +ENTRY(__smccc_workaround_smc_end_\num) +.endm + +ENTRY(__mitigate_spectre_bhb_clear_insn_start) + clearbhb + isb +ENTRY(__mitigate_spectre_bhb_clear_insn_end) + +mitigate_spectre_bhb_loop 8 +mitigate_spectre_bhb_loop 24 +mitigate_spectre_bhb_loop 32 +smccc_workaround 1, #ARM_SMCCC_ARCH_WORKAROUND_1_FID +smccc_workaround 3, #ARM_SMCCC_ARCH_WORKAROUND_3_FID /* * Local variables: --- a/xen/arch/arm/cpuerrata.c +++ b/xen/arch/arm/cpuerrata.c @@ -145,7 +145,16 @@ install_bp_hardening_vec(const struct ar return ret; } -extern char __smccc_workaround_1_smc_start[], __smccc_workaround_1_smc_end[]; +extern char __smccc_workaround_smc_start_1[], __smccc_workaround_smc_end_1[]; +extern char __smccc_workaround_smc_start_3[], __smccc_workaround_smc_end_3[]; +extern char __mitigate_spectre_bhb_clear_insn_start[], + __mitigate_spectre_bhb_clear_insn_end[]; +extern char __mitigate_spectre_bhb_loop_start_8[], + __mitigate_spectre_bhb_loop_end_8[]; +extern char __mitigate_spectre_bhb_loop_start_24[], + __mitigate_spectre_bhb_loop_end_24[]; +extern char __mitigate_spectre_bhb_loop_start_32[], + __mitigate_spectre_bhb_loop_end_32[]; static int enable_smccc_arch_workaround_1(void *data) { @@ -176,8 +185,8 @@ static int enable_smccc_arch_workaround_ if ( (int)res.a0 < 0 ) goto warn; - return !install_bp_hardening_vec(entry,__smccc_workaround_1_smc_start, - __smccc_workaround_1_smc_end, + return !install_bp_hardening_vec(entry,__smccc_workaround_smc_start_1, + __smccc_workaround_smc_end_1, "call ARM_SMCCC_ARCH_WORKAROUND_1"); warn: @@ -187,6 +196,93 @@ warn: return 0; } +/* + * Spectre BHB Mitigation + * + * CPU is either: + * - Having CVS2.3 so it is not affected. + * - Having ECBHB and is clearing the branch history buffer when an exception + * to a different exception level is happening so no mitigation is needed. + * - Mitigating using a loop on exception entry (number of loop depending on + * the CPU). + * - Mitigating using the firmware. + */ +static int enable_spectre_bhb_workaround(void *data) +{ + const struct arm_cpu_capabilities *entry = data; + + /* + * Enable callbacks are called on every CPU based on the capabilities, so + * double-check whether the CPU matches the entry. + */ + if ( !entry->matches(entry) ) + return 0; + + if ( cpu_data[smp_processor_id()].pfr64.csv2 == 3 ) + return 0; + + if ( cpu_data[smp_processor_id()].mm64.ecbhb ) + return 0; + + if ( cpu_data[smp_processor_id()].isa64.clearbhb ) + return !install_bp_hardening_vec(entry, + __mitigate_spectre_bhb_clear_insn_start, + __mitigate_spectre_bhb_clear_insn_end, + "use clearBHB instruction"); + + /* Apply solution depending on hwcaps set on arm_errata */ + if ( cpus_have_cap(ARM_WORKAROUND_BHB_LOOP_8) ) + return !install_bp_hardening_vec(entry, + __mitigate_spectre_bhb_loop_start_8, + __mitigate_spectre_bhb_loop_end_8, + "use 8 loops workaround"); + + if ( cpus_have_cap(ARM_WORKAROUND_BHB_LOOP_24) ) + return !install_bp_hardening_vec(entry, + __mitigate_spectre_bhb_loop_start_24, + __mitigate_spectre_bhb_loop_end_24, + "use 24 loops workaround"); + + if ( cpus_have_cap(ARM_WORKAROUND_BHB_LOOP_32) ) + return !install_bp_hardening_vec(entry, + __mitigate_spectre_bhb_loop_start_32, + __mitigate_spectre_bhb_loop_end_32, + "use 32 loops workaround"); + + if ( cpus_have_cap(ARM_WORKAROUND_BHB_SMCC_3) ) + { + struct arm_smccc_res res; + + if ( smccc_ver < SMCCC_VERSION(1, 1) ) + goto warn; + + arm_smccc_1_1_smc(ARM_SMCCC_ARCH_FEATURES_FID, + ARM_SMCCC_ARCH_WORKAROUND_3_FID, &res); + /* The return value is in the lower 32-bits. */ + if ( (int)res.a0 < 0 ) + { + /* + * On processor affected with CSV2=0, workaround 1 will mitigate + * both Spectre v2 and BHB so use it when available + */ + if ( enable_smccc_arch_workaround_1(data) ) + return 1; + + goto warn; + } + + return !install_bp_hardening_vec(entry,__smccc_workaround_smc_start_3, + __smccc_workaround_smc_end_3, + "call ARM_SMCCC_ARCH_WORKAROUND_3"); + } + +warn: + printk_once("**** No support for any spectre BHB workaround. ****\n" + "**** Please update your firmware. ****\n"); + + return 0; +} + #endif /* CONFIG_ARM64_HARDEN_BRANCH_PREDICTOR */ /* Hardening Branch predictor code for Arm32 */ @@ -446,19 +542,77 @@ static const struct arm_cpu_capabilities }, { .capability = ARM_HARDEN_BRANCH_PREDICTOR, - MIDR_ALL_VERSIONS(MIDR_CORTEX_A72), + MIDR_RANGE(MIDR_CORTEX_A72, 0, 1 << MIDR_VARIANT_SHIFT), .enable = enable_smccc_arch_workaround_1, }, { - .capability = ARM_HARDEN_BRANCH_PREDICTOR, + .capability = ARM_WORKAROUND_BHB_SMCC_3, MIDR_ALL_VERSIONS(MIDR_CORTEX_A73), - .enable = enable_smccc_arch_workaround_1, + .enable = enable_spectre_bhb_workaround, }, { - .capability = ARM_HARDEN_BRANCH_PREDICTOR, + .capability = ARM_WORKAROUND_BHB_SMCC_3, MIDR_ALL_VERSIONS(MIDR_CORTEX_A75), - .enable = enable_smccc_arch_workaround_1, + .enable = enable_spectre_bhb_workaround, + }, + /* spectre BHB */ + { + .capability = ARM_WORKAROUND_BHB_LOOP_8, + MIDR_RANGE(MIDR_CORTEX_A72, 1 << MIDR_VARIANT_SHIFT, + (MIDR_VARIANT_MASK | MIDR_REVISION_MASK)), + .enable = enable_spectre_bhb_workaround, + }, + { + .capability = ARM_WORKAROUND_BHB_LOOP_24, + MIDR_ALL_VERSIONS(MIDR_CORTEX_A76), + .enable = enable_spectre_bhb_workaround, + }, + { + .capability = ARM_WORKAROUND_BHB_LOOP_24, + MIDR_ALL_VERSIONS(MIDR_CORTEX_A77), + .enable = enable_spectre_bhb_workaround, + }, + { + .capability = ARM_WORKAROUND_BHB_LOOP_32, + MIDR_ALL_VERSIONS(MIDR_CORTEX_A78), + .enable = enable_spectre_bhb_workaround, + }, + { + .capability = ARM_WORKAROUND_BHB_LOOP_32, + MIDR_ALL_VERSIONS(MIDR_CORTEX_A78C), + .enable = enable_spectre_bhb_workaround, }, + { + .capability = ARM_WORKAROUND_BHB_LOOP_32, + MIDR_ALL_VERSIONS(MIDR_CORTEX_X1), + .enable = enable_spectre_bhb_workaround, + }, + { + .capability = ARM_WORKAROUND_BHB_LOOP_32, + MIDR_ALL_VERSIONS(MIDR_CORTEX_X2), + .enable = enable_spectre_bhb_workaround, + }, + { + .capability = ARM_WORKAROUND_BHB_LOOP_32, + MIDR_ALL_VERSIONS(MIDR_CORTEX_A710), + .enable = enable_spectre_bhb_workaround, + }, + { + .capability = ARM_WORKAROUND_BHB_LOOP_24, + MIDR_ALL_VERSIONS(MIDR_NEOVERSE_N1), + .enable = enable_spectre_bhb_workaround, + }, + { + .capability = ARM_WORKAROUND_BHB_LOOP_32, + MIDR_ALL_VERSIONS(MIDR_NEOVERSE_N2), + .enable = enable_spectre_bhb_workaround, + }, + { + .capability = ARM_WORKAROUND_BHB_LOOP_32, + MIDR_ALL_VERSIONS(MIDR_NEOVERSE_V1), + .enable = enable_spectre_bhb_workaround, + }, + #endif #ifdef CONFIG_ARM32_HARDEN_BRANCH_PREDICTOR { --- a/xen/include/asm-arm/arm64/macros.h +++ b/xen/include/asm-arm/arm64/macros.h @@ -27,6 +27,11 @@ sb .endm + /* clearbhb instruction clearing the branch history */ + .macro clearbhb + hint #22 + .endm + /* * Register aliases. */ --- a/xen/include/asm-arm/cpufeature.h +++ b/xen/include/asm-arm/cpufeature.h @@ -63,8 +63,12 @@ #define ARM64_WORKAROUND_AT_SPECULATE 9 #define ARM_WORKAROUND_858921 10 #define ARM64_WORKAROUND_REPEAT_TLBI 11 +#define ARM_WORKAROUND_BHB_LOOP_8 12 +#define ARM_WORKAROUND_BHB_LOOP_24 13 +#define ARM_WORKAROUND_BHB_LOOP_32 14 +#define ARM_WORKAROUND_BHB_SMCC_3 15 -#define ARM_NCAPS 12 +#define ARM_NCAPS 16 #ifndef __ASSEMBLY__ --- a/xen/include/asm-arm/smccc.h +++ b/xen/include/asm-arm/smccc.h @@ -334,6 +334,12 @@ void __arm_smccc_1_0_smc(register_t a0, ARM_SMCCC_OWNER_ARCH, \ 0x7FFF) +#define ARM_SMCCC_ARCH_WORKAROUND_3_FID \ + ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \ + ARM_SMCCC_CONV_32, \ + ARM_SMCCC_OWNER_ARCH, \ + 0x3FFF) + /* SMCCC error codes */ #define ARM_SMCCC_NOT_REQUIRED (-2) #define ARM_SMCCC_ERR_UNKNOWN_FUNCTION (-1)
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