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fix(security): optimisations for CVE-2022-23960

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Optimised the loop workaround for Spectre_BHB mitigation:
1. use of speculation barrier for cores implementing SB instruction.
2. use str/ldr instead of stp/ldp as the loop uses only X2 register.

Signed-off-by: Bipin Ravi <bipin.ravi@arm.com>
Change-Id: I8ac53ea1e42407ad8004c1d59c05f791011f195d
This commit is contained in:
Bipin Ravi 2022-10-13 17:25:51 -05:00
parent c45d2febb9
commit e74d658181
2 changed files with 17 additions and 5 deletions
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13
include/arch/aarch64/asm_macros.S
View file

@ -214,6 +214,19 @@
ret ret
.endm .endm
/*
* Macro for using speculation barrier instruction introduced by
* FEAT_SB, if it's enabled.
*/
.macro speculation_barrier
#if ENABLE_FEAT_SB
sb
#else
dsb sy
isb
#endif
.endm
/* /*
* Macro for mitigating against speculative execution beyond ERET. Uses the * Macro for mitigating against speculative execution beyond ERET. Uses the
* speculation barrier instruction introduced by FEAT_SB, if it's enabled. * speculation barrier instruction introduced by FEAT_SB, if it's enabled.

9
lib/cpus/aarch64/wa_cve_2022_23960_bhb.S
View file

@ -9,11 +9,11 @@
#if WORKAROUND_CVE_2022_23960 #if WORKAROUND_CVE_2022_23960
/* /*
* This macro applies the mitigation for CVE-2022-23960. * This macro applies the mitigation for CVE-2022-23960.
* The macro saves x2-x3 to the CPU context. * The macro saves x2 to the CPU context.
* SP should point to the CPU context. * SP should point to the CPU context.
*/ */
.macro apply_cve_2022_23960_bhb_wa _bhb_loop_count .macro apply_cve_2022_23960_bhb_wa _bhb_loop_count
stp x2, x3, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X2] str x2, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X2]
/* CVE-BHB-NUM loop count */ /* CVE-BHB-NUM loop count */
mov x2, \_bhb_loop_count mov x2, \_bhb_loop_count
@ -24,8 +24,7 @@
2: 2:
subs x2, x2, #1 subs x2, x2, #1
bne 1b bne 1b
dsb sy speculation_barrier
isb ldr x2, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X2]
ldp x2, x3, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X2]
.endm .endm
#endif /* WORKAROUND_CVE_2022_23960 */ #endif /* WORKAROUND_CVE_2022_23960 */