[PATCH 0/2] Spectre v2 tweaks

[PATCH 0/2] Spectre v2 tweaks

[David Woodhouse]

A couple of things that have been lurking in the "shall we do this?" area
of my git tree for a while, and I think we probably should...

David Woodhouse (1):
  x86/retpoline: No retpolines for built-in __init functions

KarimAllah Ahmed (1):
  x86: Simplify spectre_v2 command line parsing

 arch/x86/kernel/cpu/bugs.c | 86 ++++++++++++++++++++++++++++++----------------
 include/linux/init.h       |  9 ++++-
 2 files changed, 64 insertions(+), 31 deletions(-)

-- 
2.7.4

[PATCH 1/2] x86/retpoline: No retpolines for built-in __init functions

[David Woodhouse]

There's no point in building init code with retpolines, since it runs before
any potentially hostile userspace does. And before the retpoline is actually
ALTERNATIVEd into place, for much of it.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 include/linux/init.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/init.h b/include/linux/init.h
index ea1b311..506a981 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -5,6 +5,13 @@
 #include <linux/compiler.h>
 #include <linux/types.h>
 
+/* Built-in __init functions needn't be compiled with retpoline */
+#if defined(RETPOLINE) && !defined(MODULE)
+#define __noretpoline __attribute__((indirect_branch("keep")))
+#else
+#define __noretpoline
+#endif
+
 /* These macros are used to mark some functions or 
  * initialized data (doesn't apply to uninitialized data)
  * as `initialization' functions. The kernel can take this
@@ -40,7 +47,7 @@
 
 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init		__section(.init.text) __cold  __latent_entropy
+#define __init		__section(.init.text) __cold  __latent_entropy __noretpoline
 #define __initdata	__section(.init.data)
 #define __initconst	__section(.init.rodata)
 #define __exitdata	__section(.exit.data)
-- 
2.7.4

[PATCH 2/2] x86: Simplify spectre_v2 command line parsing

[David Woodhouse]

From: KarimAllah Ahmed <karahmed@amazon.de>

[dwmw2: Use ARRAY_SIZE]
Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 arch/x86/kernel/cpu/bugs.c | 86 ++++++++++++++++++++++++++++++----------------
 1 file changed, 56 insertions(+), 30 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index dd3a3cc..71949bf 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -119,13 +119,13 @@ static inline const char *spectre_v2_module_string(void) { return ""; }
 static void __init spec2_print_if_insecure(const char *reason)
 {
 	if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
-		pr_info("%s\n", reason);
+		pr_info("%s selected on command line.\n", reason);
 }
 
 static void __init spec2_print_if_secure(const char *reason)
 {
 	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
-		pr_info("%s\n", reason);
+		pr_info("%s selected on command line.\n", reason);
 }
 
 static inline bool retp_compiler(void)
@@ -140,42 +140,68 @@ static inline bool match_option(const char *arg, int arglen, const char *opt)
 	return len == arglen && !strncmp(arg, opt, len);
 }
 
+static const struct {
+	const char *option;
+	enum spectre_v2_mitigation_cmd cmd;
+	bool secure;
+} mitigation_options[] = {
+	{ "off",               SPECTRE_V2_CMD_NONE,              false },
+	{ "on",                SPECTRE_V2_CMD_FORCE,             true },
+	{ "retpoline",         SPECTRE_V2_CMD_RETPOLINE,         false },
+	{ "retpoline,amd",     SPECTRE_V2_CMD_RETPOLINE_AMD,     false },
+	{ "retpoline,generic", SPECTRE_V2_CMD_RETPOLINE_GENERIC, false },
+	{ "auto",              SPECTRE_V2_CMD_AUTO,              false },
+};
+
 static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
 {
 	char arg[20];
-	int ret;
-
-	ret = cmdline_find_option(boot_command_line, "spectre_v2", arg,
-				  sizeof(arg));
-	if (ret > 0)  {
-		if (match_option(arg, ret, "off")) {
-			goto disable;
-		} else if (match_option(arg, ret, "on")) {
-			spec2_print_if_secure("force enabled on command line.");
-			return SPECTRE_V2_CMD_FORCE;
-		} else if (match_option(arg, ret, "retpoline")) {
-			spec2_print_if_insecure("retpoline selected on command line.");
-			return SPECTRE_V2_CMD_RETPOLINE;
-		} else if (match_option(arg, ret, "retpoline,amd")) {
-			if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD) {
-				pr_err("retpoline,amd selected but CPU is not AMD. Switching to AUTO select\n");
-				return SPECTRE_V2_CMD_AUTO;
-			}
-			spec2_print_if_insecure("AMD retpoline selected on command line.");
-			return SPECTRE_V2_CMD_RETPOLINE_AMD;
-		} else if (match_option(arg, ret, "retpoline,generic")) {
-			spec2_print_if_insecure("generic retpoline selected on command line.");
-			return SPECTRE_V2_CMD_RETPOLINE_GENERIC;
-		} else if (match_option(arg, ret, "auto")) {
+	int ret, i;
+	enum spectre_v2_mitigation_cmd cmd = SPECTRE_V2_CMD_AUTO;
+
+	if (cmdline_find_option_bool(boot_command_line, "nospectre_v2"))
+		return SPECTRE_V2_CMD_NONE;
+	else {
+		ret = cmdline_find_option(boot_command_line, "spectre_v2", arg,
+					  sizeof(arg));
+		if (ret < 0)
+			return SPECTRE_V2_CMD_AUTO;
+
+		for (i = 0; i < ARRAY_SIZE(mitigation_options); i++) {
+			if (!match_option(arg, ret, mitigation_options[i].option))
+				continue;
+			cmd = mitigation_options[i].cmd;
+			break;
+		}
+
+		if (i >= ARRAY_SIZE(mitigation_options)) {
+			pr_err("unknown option (%s). Switching to AUTO select\n",
+			       mitigation_options[i].option);
 			return SPECTRE_V2_CMD_AUTO;
 		}
 	}
 
-	if (!cmdline_find_option_bool(boot_command_line, "nospectre_v2"))
+	if ((cmd == SPECTRE_V2_CMD_RETPOLINE ||
+	     cmd == SPECTRE_V2_CMD_RETPOLINE_AMD ||
+	     cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC) &&
+	    !IS_ENABLED(CONFIG_RETPOLINE)) {
+		pr_err("%s selected but not compiled in. Switching to AUTO select\n",
+		       mitigation_options[i].option);
 		return SPECTRE_V2_CMD_AUTO;
-disable:
-	spec2_print_if_insecure("disabled on command line.");
-	return SPECTRE_V2_CMD_NONE;
+	}
+
+	if (cmd == SPECTRE_V2_CMD_RETPOLINE_AMD &&
+	    boot_cpu_data.x86_vendor != X86_VENDOR_AMD) {
+		pr_err("retpoline,amd selected but CPU is not AMD. Switching to AUTO select\n");
+		return SPECTRE_V2_CMD_AUTO;
+	}
+
+	if (mitigation_options[i].secure)
+		spec2_print_if_secure(mitigation_options[i].option);
+	else
+		spec2_print_if_insecure(mitigation_options[i].option);
+
+	return cmd;
 }
 
 /* Check for Skylake-like CPUs (for RSB handling) */
-- 
2.7.4

[tip:x86/pti] x86/retpoline: Avoid retpolines for built-in __init functions

[tip-bot for David Woodhouse]

Commit-ID:  66f793099a636862a71c59d4a6ba91387b155e0c
Gitweb:     https://git.kernel.org/tip/66f793099a636862a71c59d4a6ba91387b155e0c
Author:     David Woodhouse <dwmw@amazon.co.uk>
AuthorDate: Thu, 1 Feb 2018 11:27:20 +0000
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 2 Feb 2018 12:28:27 +0100

x86/retpoline: Avoid retpolines for built-in __init functions

There's no point in building init code with retpolines, since it runs before
any potentially hostile userspace does. And before the retpoline is actually
ALTERNATIVEd into place, for much of it.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: karahmed@amazon.de
Cc: peterz@infradead.org
Cc: bp@alien8.de
Link: https://lkml.kernel.org/r/1517484441-1420-2-git-send-email-dwmw@amazon.co.uk

---
 include/linux/init.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/init.h b/include/linux/init.h
index ea1b311..506a981 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -5,6 +5,13 @@
 #include <linux/compiler.h>
 #include <linux/types.h>
 
+/* Built-in __init functions needn't be compiled with retpoline */
+#if defined(RETPOLINE) && !defined(MODULE)
+#define __noretpoline __attribute__((indirect_branch("keep")))
+#else
+#define __noretpoline
+#endif
+
 /* These macros are used to mark some functions or 
  * initialized data (doesn't apply to uninitialized data)
  * as `initialization' functions. The kernel can take this
@@ -40,7 +47,7 @@
 
 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init		__section(.init.text) __cold  __latent_entropy
+#define __init		__section(.init.text) __cold  __latent_entropy __noretpoline
 #define __initdata	__section(.init.data)
 #define __initconst	__section(.init.rodata)
 #define __exitdata	__section(.exit.data)

[tip:x86/pti] x86/spectre: Simplify spectre_v2 command line parsing

[tip-bot for KarimAllah Ahmed]

Commit-ID:  9005c6834c0ffdfe46afa76656bd9276cca864f6
Gitweb:     https://git.kernel.org/tip/9005c6834c0ffdfe46afa76656bd9276cca864f6
Author:     KarimAllah Ahmed <karahmed@amazon.de>
AuthorDate: Thu, 1 Feb 2018 11:27:21 +0000
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 2 Feb 2018 12:28:27 +0100

x86/spectre: Simplify spectre_v2 command line parsing

[dwmw2: Use ARRAY_SIZE]

Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: peterz@infradead.org
Cc: bp@alien8.de
Link: https://lkml.kernel.org/r/1517484441-1420-3-git-send-email-dwmw@amazon.co.uk

---
 arch/x86/kernel/cpu/bugs.c | 86 ++++++++++++++++++++++++++++++----------------
 1 file changed, 56 insertions(+), 30 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index dd3a3cc..71949bf 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -119,13 +119,13 @@ static inline const char *spectre_v2_module_string(void) { return ""; }
 static void __init spec2_print_if_insecure(const char *reason)
 {
 	if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
-		pr_info("%s\n", reason);
+		pr_info("%s selected on command line.\n", reason);
 }
 
 static void __init spec2_print_if_secure(const char *reason)
 {
 	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
-		pr_info("%s\n", reason);
+		pr_info("%s selected on command line.\n", reason);
 }
 
 static inline bool retp_compiler(void)
@@ -140,42 +140,68 @@ static inline bool match_option(const char *arg, int arglen, const char *opt)
 	return len == arglen && !strncmp(arg, opt, len);
 }
 
+static const struct {
+	const char *option;
+	enum spectre_v2_mitigation_cmd cmd;
+	bool secure;
+} mitigation_options[] = {
+	{ "off",               SPECTRE_V2_CMD_NONE,              false },
+	{ "on",                SPECTRE_V2_CMD_FORCE,             true },
+	{ "retpoline",         SPECTRE_V2_CMD_RETPOLINE,         false },
+	{ "retpoline,amd",     SPECTRE_V2_CMD_RETPOLINE_AMD,     false },
+	{ "retpoline,generic", SPECTRE_V2_CMD_RETPOLINE_GENERIC, false },
+	{ "auto",              SPECTRE_V2_CMD_AUTO,              false },
+};
+
 static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
 {
 	char arg[20];
-	int ret;
-
-	ret = cmdline_find_option(boot_command_line, "spectre_v2", arg,
-				  sizeof(arg));
-	if (ret > 0)  {
-		if (match_option(arg, ret, "off")) {
-			goto disable;
-		} else if (match_option(arg, ret, "on")) {
-			spec2_print_if_secure("force enabled on command line.");
-			return SPECTRE_V2_CMD_FORCE;
-		} else if (match_option(arg, ret, "retpoline")) {
-			spec2_print_if_insecure("retpoline selected on command line.");
-			return SPECTRE_V2_CMD_RETPOLINE;
-		} else if (match_option(arg, ret, "retpoline,amd")) {
-			if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD) {
-				pr_err("retpoline,amd selected but CPU is not AMD. Switching to AUTO select\n");
-				return SPECTRE_V2_CMD_AUTO;
-			}
-			spec2_print_if_insecure("AMD retpoline selected on command line.");
-			return SPECTRE_V2_CMD_RETPOLINE_AMD;
-		} else if (match_option(arg, ret, "retpoline,generic")) {
-			spec2_print_if_insecure("generic retpoline selected on command line.");
-			return SPECTRE_V2_CMD_RETPOLINE_GENERIC;
-		} else if (match_option(arg, ret, "auto")) {
+	int ret, i;
+	enum spectre_v2_mitigation_cmd cmd = SPECTRE_V2_CMD_AUTO;
+
+	if (cmdline_find_option_bool(boot_command_line, "nospectre_v2"))
+		return SPECTRE_V2_CMD_NONE;
+	else {
+		ret = cmdline_find_option(boot_command_line, "spectre_v2", arg,
+					  sizeof(arg));
+		if (ret < 0)
+			return SPECTRE_V2_CMD_AUTO;
+
+		for (i = 0; i < ARRAY_SIZE(mitigation_options); i++) {
+			if (!match_option(arg, ret, mitigation_options[i].option))
+				continue;
+			cmd = mitigation_options[i].cmd;
+			break;
+		}
+
+		if (i >= ARRAY_SIZE(mitigation_options)) {
+			pr_err("unknown option (%s). Switching to AUTO select\n",
+			       mitigation_options[i].option);
 			return SPECTRE_V2_CMD_AUTO;
 		}
 	}
 
-	if (!cmdline_find_option_bool(boot_command_line, "nospectre_v2"))
+	if ((cmd == SPECTRE_V2_CMD_RETPOLINE ||
+	     cmd == SPECTRE_V2_CMD_RETPOLINE_AMD ||
+	     cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC) &&
+	    !IS_ENABLED(CONFIG_RETPOLINE)) {
+		pr_err("%s selected but not compiled in. Switching to AUTO select\n",
+		       mitigation_options[i].option);
 		return SPECTRE_V2_CMD_AUTO;
-disable:
-	spec2_print_if_insecure("disabled on command line.");
-	return SPECTRE_V2_CMD_NONE;
+	}
+
+	if (cmd == SPECTRE_V2_CMD_RETPOLINE_AMD &&
+	    boot_cpu_data.x86_vendor != X86_VENDOR_AMD) {
+		pr_err("retpoline,amd selected but CPU is not AMD. Switching to AUTO select\n");
+		return SPECTRE_V2_CMD_AUTO;
+	}
+
+	if (mitigation_options[i].secure)
+		spec2_print_if_secure(mitigation_options[i].option);
+	else
+		spec2_print_if_insecure(mitigation_options[i].option);
+
+	return cmd;
 }
 
 /* Check for Skylake-like CPUs (for RSB handling) */