From: Pawan Gupta Date: Mon, 5 May 2025 21:35:12 +0000 (-0700) Subject: x86/bhi: Do not set BHI_DIS_S in 32-bit mode X-Git-Tag: v6.15-rc7~42^2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=073fdbe02c69c43fb7c0d547ec265c7747d4a646;p=thirdparty%2Fkernel%2Flinux.git x86/bhi: Do not set BHI_DIS_S in 32-bit mode 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 --- diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 362602b705cc4..f219f0f4f2d11 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1697,11 +1697,11 @@ static void __init bhi_select_mitigation(void) return; } - /* Mitigate in hardware if supported */ - 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; if (bhi_mitigation == BHI_MITIGATION_VMEXIT_ONLY) { diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index e472572392ef6..8a0fabb850b77 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1527,8 +1527,7 @@ 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 @@ -1538,6 +1537,8 @@ 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 */ }