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arm64: Use the clearbhb instruction in mitigations

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commit 228a26b912287934789023b4132ba76065d9491c upstream.

Future CPUs may implement a clearbhb instruction that is sufficient
to mitigate SpectreBHB. CPUs that implement this instruction, but
not CSV2.3 must be affected by Spectre-BHB.

Add support to use this instruction as the BHB mitigation on CPUs
that support it. The instruction is in the hint space, so it will
be treated by a NOP as older CPUs.

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
[ modified for stable: Use a KVM vector template instead of alternatives,
  removed bitmap of mitigations ]
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
James Morse 2022-03-15 18:24:15 +00:00 committed by Greg Kroah-Hartman
parent fb65675f66
commit 970a21404e
8 changed files with 57 additions and 0 deletions
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7
arch/arm64/include/asm/assembler.h
View File

@ -110,6 +110,13 @@
hint #20
.endm
/*
* Clear Branch History instruction
*/
.macro clearbhb
hint #22
.endm
/*
* Speculation barrier
*/

13
arch/arm64/include/asm/cpufeature.h
View File

@ -523,6 +523,19 @@ static inline bool supports_csv2p3(int scope)
return csv2_val == 3;
}
static inline bool supports_clearbhb(int scope)
{
u64 isar2;
if (scope == SCOPE_LOCAL_CPU)
isar2 = read_sysreg_s(SYS_ID_AA64ISAR2_EL1);
else
isar2 = read_sanitised_ftr_reg(SYS_ID_AA64ISAR2_EL1);
return cpuid_feature_extract_unsigned_field(isar2,
ID_AA64ISAR2_CLEARBHB_SHIFT);
}
static inline bool system_supports_32bit_el0(void)
{
return cpus_have_const_cap(ARM64_HAS_32BIT_EL0);

1
arch/arm64/include/asm/sysreg.h
View File

@ -577,6 +577,7 @@
#define ID_AA64ISAR1_GPI_IMP_DEF 0x1
/* id_aa64isar2 */
#define ID_AA64ISAR2_CLEARBHB_SHIFT 28
#define ID_AA64ISAR2_RPRES_SHIFT 4
#define ID_AA64ISAR2_WFXT_SHIFT 0

7
arch/arm64/include/asm/vectors.h
View File

@ -32,6 +32,12 @@ enum arm64_bp_harden_el1_vectors {
* canonical vectors.
*/
EL1_VECTOR_BHB_FW,
/*
* Use the ClearBHB instruction, before branching to the canonical
* vectors.
*/
EL1_VECTOR_BHB_CLEAR_INSN,
#endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */
/*
@ -43,6 +49,7 @@ enum arm64_bp_harden_el1_vectors {
#ifndef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY
#define EL1_VECTOR_BHB_LOOP -1
#define EL1_VECTOR_BHB_FW -1
#define EL1_VECTOR_BHB_CLEAR_INSN -1
#endif /* !CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */
/* The vectors to use on return from EL0. e.g. to remap the kernel */

14
arch/arm64/kernel/cpu_errata.c
View File

@ -125,6 +125,8 @@ 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[];
extern char __spectre_bhb_clearbhb_start[];
extern char __spectre_bhb_clearbhb_end[];
static void __copy_hyp_vect_bpi(int slot, const char *hyp_vecs_start,
const char *hyp_vecs_end)
@ -1086,6 +1088,7 @@ static void update_mitigation_state(enum mitigation_state *oldp,
* - Mitigated by a branchy loop a CPU specific number of times, and listed
* in our "loop mitigated list".
* - Mitigated in software by the firmware Spectre v2 call.
* - Has the ClearBHB instruction to perform the mitigation.
* - Has the 'Exception Clears Branch History Buffer' (ECBHB) feature, so no
* software mitigation in the vectors is needed.
* - Has CSV2.3, so is unaffected.
@ -1226,6 +1229,9 @@ 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;
@ -1266,6 +1272,8 @@ static const char *kvm_bhb_get_vecs_end(const char *start)
return __spectre_bhb_loop_k24_end;
else if (start == __spectre_bhb_loop_k32_start)
return __spectre_bhb_loop_k32_end;
else if (start == __spectre_bhb_clearbhb_start)
return __spectre_bhb_clearbhb_end;
return NULL;
}
@ -1305,6 +1313,7 @@ static void kvm_setup_bhb_slot(const char *hyp_vecs_start)
#define __spectre_bhb_loop_k8_start NULL
#define __spectre_bhb_loop_k24_start NULL
#define __spectre_bhb_loop_k32_start NULL
#define __spectre_bhb_clearbhb_start NULL
static void kvm_setup_bhb_slot(const char *hyp_vecs_start) { }
#endif
@ -1323,6 +1332,11 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
} else if (cpu_mitigations_off()) {
pr_info_once("spectre-bhb mitigation disabled by command line option\n");
} else if (supports_ecbhb(SCOPE_LOCAL_CPU)) {
state = SPECTRE_MITIGATED;
} else if (supports_clearbhb(SCOPE_LOCAL_CPU)) {
kvm_setup_bhb_slot(__spectre_bhb_clearbhb_start);
this_cpu_set_vectors(EL1_VECTOR_BHB_CLEAR_INSN);
state = SPECTRE_MITIGATED;
} else if (spectre_bhb_loop_affected(SCOPE_LOCAL_CPU)) {
switch (spectre_bhb_loop_affected(SCOPE_SYSTEM)) {

1
arch/arm64/kernel/cpufeature.c
View File

@ -156,6 +156,7 @@ static const struct arm64_ftr_bits ftr_id_aa64isar1[] = {
};
static const struct arm64_ftr_bits ftr_id_aa64isar2[] = {
ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_HIGHER_SAFE, ID_AA64ISAR2_CLEARBHB_SHIFT, 4, 0),
ARM64_FTR_END,
};

8
arch/arm64/kernel/entry.S
View File

@ -1074,6 +1074,7 @@ alternative_else_nop_endif
#define BHB_MITIGATION_NONE 0
#define BHB_MITIGATION_LOOP 1
#define BHB_MITIGATION_FW 2
#define BHB_MITIGATION_INSN 3
.macro tramp_ventry, vector_start, regsize, kpti, bhb
.align 7
@ -1090,6 +1091,11 @@ alternative_else_nop_endif
__mitigate_spectre_bhb_loop x30
.endif // \bhb == BHB_MITIGATION_LOOP
.if \bhb == BHB_MITIGATION_INSN
clearbhb
isb
.endif // \bhb == BHB_MITIGATION_INSN
.if \kpti == 1
/*
* Defend against branch aliasing attacks by pushing a dummy
@ -1170,6 +1176,7 @@ ENTRY(tramp_vectors)
#ifdef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY
generate_tramp_vector kpti=1, bhb=BHB_MITIGATION_LOOP
generate_tramp_vector kpti=1, bhb=BHB_MITIGATION_FW
generate_tramp_vector kpti=1, bhb=BHB_MITIGATION_INSN
#endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */
generate_tramp_vector kpti=1, bhb=BHB_MITIGATION_NONE
END(tramp_vectors)
@ -1232,6 +1239,7 @@ SYM_CODE_START(__bp_harden_el1_vectors)
#ifdef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY
generate_el1_vector bhb=BHB_MITIGATION_LOOP
generate_el1_vector bhb=BHB_MITIGATION_FW
generate_el1_vector bhb=BHB_MITIGATION_INSN
#endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */
SYM_CODE_END(__bp_harden_el1_vectors)
.popsection

6
arch/arm64/kvm/hyp/hyp-entry.S
View File

@ -405,4 +405,10 @@ ENTRY(__spectre_bhb_loop_k32_start)
ldp x0, x1, [sp, #(8 * 0)]
add sp, sp, #(8 * 2)
ENTRY(__spectre_bhb_loop_k32_end)
ENTRY(__spectre_bhb_clearbhb_start)
esb
clearbhb
isb
ENTRY(__spectre_bhb_clearbhb_end)
#endif