x86/srso: Fix srso_show_state() side effect

jpoimboe · bp3tk0v · commit a8cf700c17d9 · 2023-09-19T10:53:34.000+02:00
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: fb3bd91 ("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
diff --git 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)

Original file line number	Diff line number	Diff line change
`@@ -2717,7 +2717,7 @@ static ssize_t srso_show_state(char *buf)`
`2717`	`2717`
`2718`	`2718`	`return sysfs_emit(buf, "%s%s\n",`
`2719`	`2719`	`srso_strings[srso_mitigation],`
`2720`		`- (cpu_has_ibpb_brtype_microcode() ? "" : ", no microcode"));`
	`2720`	`+ boot_cpu_has(X86_FEATURE_IBPB_BRTYPE) ? "" : ", no microcode");`
`2721`	`2721`	`}`
`2722`	`2722`
`2723`	`2723`	`static ssize_t gds_show_state(char *buf)`