From ba2689234be92024e5635d30fe744f4853ad97db Mon Sep 17 00:00:00 2001 From: James Morse Date: Thu, 18 Nov 2021 13:59:46 +0000 Subject: arm64: entry: Add vectors that have the bhb mitigation sequences Some CPUs affected by Spectre-BHB need a sequence of branches, or a firmware call to be run before any indirect branch. This needs to go in the vectors. No CPU needs both. While this can be patched in, it would run on all CPUs as there is a single set of vectors. If only one part of a big/little combination is affected, the unaffected CPUs have to run the mitigation too. Create extra vectors that include the sequence. Subsequent patches will allow affected CPUs to select this set of vectors. Later patches will modify the loop count to match what the CPU requires. Reviewed-by: Catalin Marinas Signed-off-by: James Morse --- arch/arm64/include/asm/assembler.h | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) (limited to 'arch/arm64/include/asm/assembler.h') diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h index e8bd0af0141c..046c38ee2841 100644 --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -850,4 +850,28 @@ alternative_endif #endif /* GNU_PROPERTY_AARCH64_FEATURE_1_DEFAULT */ + .macro __mitigate_spectre_bhb_loop tmp +#ifdef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY + mov \tmp, #32 +.Lspectre_bhb_loop\@: + b . + 4 + subs \tmp, \tmp, #1 + b.ne .Lspectre_bhb_loop\@ + sb +#endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */ + .endm + + /* Save/restores x0-x3 to the stack */ + .macro __mitigate_spectre_bhb_fw +#ifdef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY + stp x0, x1, [sp, #-16]! + stp x2, x3, [sp, #-16]! + mov w0, #ARM_SMCCC_ARCH_WORKAROUND_3 +alternative_cb smccc_patch_fw_mitigation_conduit + nop // Patched to SMC/HVC #0 +alternative_cb_end + ldp x2, x3, [sp], #16 + ldp x0, x1, [sp], #16 +#endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */ + .endm #endif /* __ASM_ASSEMBLER_H */ -- cgit From 558c303c9734af5a813739cd284879227f7297d2 Mon Sep 17 00:00:00 2001 From: James Morse Date: Wed, 10 Nov 2021 14:48:00 +0000 Subject: arm64: Mitigate spectre style branch history side channels Speculation attacks against some high-performance processors can make use of branch history to influence future speculation. When taking an exception from user-space, a sequence of branches or a firmware call overwrites or invalidates the branch history. The sequence of branches is added to the vectors, and should appear before the first indirect branch. For systems using KPTI the sequence is added to the kpti trampoline where it has a free register as the exit from the trampoline is via a 'ret'. For systems not using KPTI, the same register tricks are used to free up a register in the vectors. For the firmware call, arch-workaround-3 clobbers 4 registers, so there is no choice but to save them to the EL1 stack. This only happens for entry from EL0, so if we take an exception due to the stack access, it will not become re-entrant. For KVM, the existing branch-predictor-hardening vectors are used. When a spectre version of these vectors is in use, the firmware call is sufficient to mitigate against Spectre-BHB. For the non-spectre versions, the sequence of branches is added to the indirect vector. Reviewed-by: Catalin Marinas Signed-off-by: James Morse --- arch/arm64/include/asm/assembler.h | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) (limited to 'arch/arm64/include/asm/assembler.h') diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h index 046c38ee2841..5cc97130843f 100644 --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -852,7 +852,9 @@ alternative_endif .macro __mitigate_spectre_bhb_loop tmp #ifdef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY - mov \tmp, #32 +alternative_cb spectre_bhb_patch_loop_iter + mov \tmp, #32 // Patched to correct the immediate +alternative_cb_end .Lspectre_bhb_loop\@: b . + 4 subs \tmp, \tmp, #1 @@ -861,6 +863,16 @@ alternative_endif #endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */ .endm + .macro mitigate_spectre_bhb_loop tmp +#ifdef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY +alternative_cb spectre_bhb_patch_loop_mitigation_enable + b .L_spectre_bhb_loop_done\@ // Patched to NOP +alternative_cb_end + __mitigate_spectre_bhb_loop \tmp +.L_spectre_bhb_loop_done\@: +#endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */ + .endm + /* Save/restores x0-x3 to the stack */ .macro __mitigate_spectre_bhb_fw #ifdef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY -- cgit From 228a26b912287934789023b4132ba76065d9491c Mon Sep 17 00:00:00 2001 From: James Morse Date: Fri, 10 Dec 2021 14:32:56 +0000 Subject: arm64: Use the clearbhb instruction in mitigations 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) Reviewed-by: Catalin Marinas Signed-off-by: James Morse --- arch/arm64/include/asm/assembler.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'arch/arm64/include/asm/assembler.h') diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h index 5cc97130843f..6ebdc0f834a7 100644 --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -108,6 +108,13 @@ hint #20 .endm +/* + * Clear Branch History instruction + */ + .macro clearbhb + hint #22 + .endm + /* * Speculation barrier */ @@ -884,6 +891,16 @@ alternative_cb smccc_patch_fw_mitigation_conduit alternative_cb_end ldp x2, x3, [sp], #16 ldp x0, x1, [sp], #16 +#endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */ + .endm + + .macro mitigate_spectre_bhb_clear_insn +#ifdef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY +alternative_cb spectre_bhb_patch_clearbhb + /* Patched to NOP when not supported */ + clearbhb + isb +alternative_cb_end #endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */ .endm #endif /* __ASM_ASSEMBLER_H */ -- cgit