x86/fpu: Allow multiple bits in clearcpuid= parameter

[ Upstream commit 0a4bb5e ] Commit 0c2a391 ("x86/fpu: Parse clearcpuid= as early XSAVE argument") changed clearcpuid parsing from __setup() to cmdline_find_option(). While the __setup() function would have been called for each clearcpuid= parameter on the command line, cmdline_find_option() will only return the last one, so the change effectively made it impossible to disable more than one bit. Allow a comma-separated list of bit numbers as the argument for clearcpuid to allow multiple bits to be disabled again. Log the bits being disabled for informational purposes. Also fix the check on the return value of cmdline_find_option(). It returns -1 when the option is not found, so testing as a boolean is incorrect. Fixes: 0c2a391 ("x86/fpu: Parse clearcpuid= as early XSAVE argument") Signed-off-by: Arvind Sankar <[email protected]> Signed-off-by: Borislav Petkov <[email protected]> Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: Sasha Levin <[email protected]>
openbmc · Oct 29, 2020 · b45c14f · b45c14f
1 parent 4f596c7
commit b45c14f
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Showing 2 changed files with 23 additions and 9 deletions.
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
@@ -577,7 +577,7 @@
 			loops can be debugged more effectively on production
 			systems.
 
-	clearcpuid=BITNUM [X86]
+	clearcpuid=BITNUM[,BITNUM...] [X86]
 			Disable CPUID feature X for the kernel. See
 			arch/x86/include/asm/cpufeatures.h for the valid bit
 			numbers. Note the Linux specific bits are not necessarily

diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
@@ -243,9 +243,9 @@ static void __init fpu__init_system_ctx_switch(void)
  */
 static void __init fpu__init_parse_early_param(void)
 {
-	char arg[32];
+	char arg[128];
 	char *argptr = arg;
-	int bit;
+	int arglen, res, bit;
 
 #ifdef CONFIG_X86_32
 	if (cmdline_find_option_bool(boot_command_line, "no387"))
@@ -268,12 +268,26 @@ static void __init fpu__init_parse_early_param(void)
 	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
 		setup_clear_cpu_cap(X86_FEATURE_XSAVES);
 
-	if (cmdline_find_option(boot_command_line, "clearcpuid", arg,
-				sizeof(arg)) &&
-	    get_option(&argptr, &bit) &&
-	    bit >= 0 &&
-	    bit < NCAPINTS * 32)
-		setup_clear_cpu_cap(bit);
+	arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
+	if (arglen <= 0)
+		return;
+
+	pr_info("Clearing CPUID bits:");
+	do {
+		res = get_option(&argptr, &bit);
+		if (res == 0 || res == 3)
+			break;
+
+		/* If the argument was too long, the last bit may be cut off */
+		if (res == 1 && arglen >= sizeof(arg))
+			break;
+
+		if (bit >= 0 && bit < NCAPINTS * 32) {
+			pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit));
+			setup_clear_cpu_cap(bit);
+		}
+	} while (res == 2);
+	pr_cont("\n");
 }
 
 /*