x86/srso: Fix srso_show_state() side effect

[ Upstream commit a8cf700c17d9ca6cb8ee7dc5c9330dbac3948237 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 3a893ab..5f38d60 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2692,7 +2692,7 @@ 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 cpu_show_common(struct device *dev, struct device_attribute *attr,