linux-kernel - [tip: x86/urgent] x86/amd: Use IBPB for firmware calls

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Date:   Tue, 19 Jul 2022 19:45:49 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/amd: Use IBPB for firmware calls

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     28a99e95f55c61855983d36a88c05c178d966bb7
Gitweb:        https://git.kernel.org/tip/28a99e95f55c61855983d36a88c05c178d966bb7
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Mon, 18 Jul 2022 13:41:37 +02:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Mon, 18 Jul 2022 15:38:09 +02:00

x86/amd: Use IBPB for firmware calls

On AMD IBRS does not prevent Retbleed; as such use IBPB before a
firmware call to flush the branch history state.

And because in order to do an EFI call, the kernel maps a whole lot of
the kernel page table into the EFI page table, do an IBPB just in case
in order to prevent the scenario of poisoning the BTB and causing an EFI
call using the unprotected RET there.

  [ bp: Massage. ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Link: https://lore.kernel.org/r/20220715194550.793957-1-cascardo@canonical.com
---
 arch/x86/include/asm/cpufeatures.h   |  1 +
 arch/x86/include/asm/nospec-branch.h |  2 ++
 arch/x86/kernel/cpu/bugs.c           | 11 ++++++++++-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 00f5227..a77b915 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -302,6 +302,7 @@
 #define X86_FEATURE_RETPOLINE_LFENCE	(11*32+13) /* "" Use LFENCE for Spectre variant 2 */
 #define X86_FEATURE_RETHUNK		(11*32+14) /* "" Use REturn THUNK */
 #define X86_FEATURE_UNRET		(11*32+15) /* "" AMD BTB untrain return */
+#define X86_FEATURE_USE_IBPB_FW		(11*32+16) /* "" Use IBPB during runtime firmware calls */
 
 /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
 #define X86_FEATURE_AVX_VNNI		(12*32+ 4) /* AVX VNNI instructions */
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 10a3bfc..38a3e86 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -297,6 +297,8 @@ do {									\
 	alternative_msr_write(MSR_IA32_SPEC_CTRL,			\
 			      spec_ctrl_current() | SPEC_CTRL_IBRS,	\
 			      X86_FEATURE_USE_IBRS_FW);			\
+	alternative_msr_write(MSR_IA32_PRED_CMD, PRED_CMD_IBPB,		\
+			      X86_FEATURE_USE_IBPB_FW);			\
 } while (0)
 
 #define firmware_restrict_branch_speculation_end()			\
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index aa34f90..78c9082 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1516,7 +1516,16 @@ static void __init spectre_v2_select_mitigation(void)
 	 * the CPU supports Enhanced IBRS, kernel might un-intentionally not
 	 * enable IBRS around firmware calls.
 	 */
-	if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_ibrs_mode(mode)) {
+	if (boot_cpu_has_bug(X86_BUG_RETBLEED) &&
+	    (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
+	     boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)) {
+
+		if (retbleed_cmd != RETBLEED_CMD_IBPB) {
+			setup_force_cpu_cap(X86_FEATURE_USE_IBPB_FW);
+			pr_info("Enabling Speculation Barrier for firmware calls\n");
+		}
+
+	} else if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_ibrs_mode(mode)) {
 		setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
 		pr_info("Enabling Restricted Speculation for firmware calls\n");
 	}