[PATCH 5.15 54/54] x86/bhi: Do not set BHI_DIS_S in 32-bit mode

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>

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 <jpoimboe@kernel.org>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kernel/cpu/bugs.c  |    5 +++--
 arch/x86/net/bpf_jit_comp.c |    5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1656,10 +1656,11 @@ static void __init bhi_select_mitigation
 			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 */
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -956,8 +956,7 @@ static int emit_spectre_bhb_barrier(u8 *
 	/* 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
@@ -967,6 +966,8 @@ static int emit_spectre_bhb_barrier(u8 *
 		 * 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 */
 	}