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Date:   Tue, 19 Sep 2023 09:45:06 -0000
From:   "tip-bot2 for Josh Poimboeuf" <tip-bot2@linutronix.de>
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Subject: [tip: x86/urgent] x86/srso: Fix srso_show_state() side effect
Cc:     Josh Poimboeuf <jpoimboe@kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Borislav Petkov (AMD)" <bp@alien8.de>,
        Nikolay Borisov <nik.borisov@suse.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org
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The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     a8cf700c17d9ca6cb8ee7dc5c9330dbac3948237
Gitweb:        https://git.kernel.org/tip/a8cf700c17d9ca6cb8ee7dc5c9330dbac3948237
Author:        Josh Poimboeuf <jpoimboe@kernel.org>
AuthorDate:    Mon, 04 Sep 2023 22:04:45 -07:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 19 Sep 2023 10:53:34 +02:00

x86/srso: Fix srso_show_state() side effect

Reading the 'spec_rstack_overflow' sysfs file can trigger an unnecessary
MSR write, and possibly even a (handled) exception if the microcode
hasn't been updated.

Avoid all that by just checking X86_FEATURE_IBPB_BRTYPE instead, which
gets set by srso_select_mitigation() if the updated microcode exists.

Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/27d128899cb8aee9eb2b57ddc996742b0c1d776b.1693889988.git.jpoimboe@kernel.org
---
 arch/x86/kernel/cpu/bugs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index f081d26..bdd3e29 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2717,7 +2717,7 @@ static ssize_t srso_show_state(char *buf)
 
 	return sysfs_emit(buf, "%s%s\n",
 			  srso_strings[srso_mitigation],
-			  (cpu_has_ibpb_brtype_microcode() ? "" : ", no microcode"));
+			  boot_cpu_has(X86_FEATURE_IBPB_BRTYPE) ? "" : ", no microcode");
 }
 
 static ssize_t gds_show_state(char *buf)