From a8a8826bf6559b1106699bc4e92ac4e15770301b Mon Sep 17 00:00:00 2001 From: Pawan Gupta Date: Mon, 5 May 2025 14:35:12 -0700 Subject: [PATCH] x86/bhi: Do not set BHI_DIS_S in 32-bit mode commit 073fdbe02c69c43fb7c0d547ec265c7747d4a646 upstream. With the possibility of intra-mode BHI via cBPF, complete mitigation for BHI is to use IBHF (history fence) instruction with BHI_DIS_S set. Since this new instruction is only available in 64-bit mode, setting BHI_DIS_S in 32-bit mode is only a partial mitigation. Do not set BHI_DIS_S in 32-bit mode so as to avoid reporting misleading mitigated status. With this change IBHF won't be used in 32-bit mode, also remove the CONFIG_X86_64 check from emit_spectre_bhb_barrier(). Suggested-by: Josh Poimboeuf Signed-off-by: Pawan Gupta Signed-off-by: Dave Hansen Reviewed-by: Josh Poimboeuf Reviewed-by: Alexandre Chartre Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/bugs.c | 5 +++-- arch/x86/net/bpf_jit_comp.c | 5 +++-- 2 files changed, 6 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 78545f7e9cc6..51f58776765b 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1677,10 +1677,11 @@ static void __init bhi_select_mitigation(void) return; } - if (spec_ctrl_bhi_dis()) + if (!IS_ENABLED(CONFIG_X86_64)) return; - if (!IS_ENABLED(CONFIG_X86_64)) + /* Mitigate in hardware if supported */ + if (spec_ctrl_bhi_dis()) return; /* Mitigate KVM by default */ diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 2f93555a1745..5a3ce74d132b 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1097,8 +1097,7 @@ static int emit_spectre_bhb_barrier(u8 **pprog, u8 *ip, /* Insert IBHF instruction */ if ((cpu_feature_enabled(X86_FEATURE_CLEAR_BHB_LOOP) && cpu_feature_enabled(X86_FEATURE_HYPERVISOR)) || - (cpu_feature_enabled(X86_FEATURE_CLEAR_BHB_HW) && - IS_ENABLED(CONFIG_X86_64))) { + cpu_feature_enabled(X86_FEATURE_CLEAR_BHB_HW)) { /* * Add an Indirect Branch History Fence (IBHF). IBHF acts as a * fence preventing branch history from before the fence from @@ -1108,6 +1107,8 @@ static int emit_spectre_bhb_barrier(u8 **pprog, u8 *ip, * hardware that doesn't need or support it. The REP and REX.W * prefixes are required by the microcode, and they also ensure * that the NOP is unlikely to be used in existing code. + * + * IBHF is not a valid instruction in 32-bit mode. */ EMIT5(0xF3, 0x48, 0x0F, 0x1E, 0xF8); /* ibhf */ }