From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Thu, 1 Feb 2018 17:25:54 +0000 (-0500)
Subject: x86/spectre_v2: Don't allow {ibrs,ipbp,lfence}_enabled to be toggled if retpoline
X-Git-Tag: v4.1.12-124.31.3~1164
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=a152f9821dc56887544d287649c1d727e56567d7;p=users%2Fjedix%2Flinux-maple.git

x86/spectre_v2: Don't allow {ibrs,ipbp,lfence}_enabled to be toggled if retpoline

is enabled.

And also refresh the spectre_v2_enabled mode depending on whether
the sysfs knobs are turned on/off.

Preserve the ability to tweak IBPB if retpoline is enabled.

Orabug: 27477743
CVE: CVE-2017-5715

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Pavel Tatashin <pasha.tatashin@oracle.com>
---

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 540dd04d58f8..1d70864c19b0 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -982,5 +982,6 @@ void df_debug(struct pt_regs *regs, long error_code);
 
 void disable_retpoline(void);
 bool retpoline_enabled(void);
+int refresh_set_spectre_v2_enabled(void);
 
 #endif /* _ASM_X86_PROCESSOR_H */
diff --git a/arch/x86/kernel/cpu/bugs_64.c b/arch/x86/kernel/cpu/bugs_64.c
index dc062b3e5597..a363f9cab12d 100644
--- a/arch/x86/kernel/cpu/bugs_64.c
+++ b/arch/x86/kernel/cpu/bugs_64.c
@@ -134,6 +134,27 @@ bool retpoline_enabled(void)
 	return false;
 }
 
+int refresh_set_spectre_v2_enabled(void)
+{
+	if (retpoline_enabled())
+		return false;
+
+	if (check_ibrs_inuse())
+		spectre_v2_enabled = SPECTRE_V2_IBRS;
+	else {
+		/*
+		 * If that didn't work (say no microcode or noibrs), we end up using
+		 * lfence on system calls/exceptions/parameters.
+		 */
+		if (lfence_inuse)
+			spectre_v2_enabled = SPECTRE_V2_IBRS_LFENCE;
+		else
+			spectre_v2_enabled = SPECTRE_V2_NONE;
+	}
+
+	return true;
+}
+
 static void __init spec2_print_if_insecure(const char *reason)
 {
 	if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
@@ -377,9 +398,7 @@ ssize_t cpu_show_spectre_v2(struct device *dev,
 	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
 		return sprintf(buf, "Not affected\n");
 
-	return sprintf(buf, "%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
-					ibrs_inuse ? "" /* As spectre_v2_strings has it. */ :
-						lfence_inuse ? " lfence " : "",
+	return sprintf(buf, "%s%s\n", spectre_v2_strings[spectre_v2_enabled],
 					ibpb_inuse ? ", IBPB" : "");
 }
 #endif
diff --git a/arch/x86/kernel/cpu/spec_ctrl.c b/arch/x86/kernel/cpu/spec_ctrl.c
index 9450e116bf59..93aa00cede93 100644
--- a/arch/x86/kernel/cpu/spec_ctrl.c
+++ b/arch/x86/kernel/cpu/spec_ctrl.c
@@ -56,6 +56,11 @@ static ssize_t ibrs_enabled_write(struct file *file,
 	if (!ibrs_supported)
 		return -ENODEV;
 
+	if (retpoline_enabled()) {
+		pr_warn("retpoline is enabled. Ignoring request to change ibrs state.\n");
+		return -EINVAL;
+	}
+
         len = min(count, sizeof(buf) - 1);
         if (copy_from_user(buf, user_buf, len))
                 return -EFAULT;
@@ -80,6 +85,7 @@ static ssize_t ibrs_enabled_write(struct file *file,
 	} else {
 		clear_ibrs_disabled();
 	}
+	refresh_set_spectre_v2_enabled();
 
 	mutex_unlock(&spec_ctrl_mutex);
 	return count;
@@ -130,6 +136,8 @@ static ssize_t ibpb_enabled_write(struct file *file,
 	else
 		clear_ibpb_disabled();
 
+	refresh_set_spectre_v2_enabled();
+
 	mutex_unlock(&spec_ctrl_mutex);
 	return count;
 }
@@ -160,8 +168,9 @@ static ssize_t lfence_enabled_write(struct file *file,
 	unsigned int enable;
 
 	/* You have to disable IBRS first. */
-	if (ibrs_inuse) {
-		pr_warn("IBRS is enabled. Ignoring request to change lfence_enabled state.");
+	if (ibrs_inuse || retpoline_enabled()) {
+		pr_warn("%s is enabled. Ignoring request to change lfence_enabled state.\n",
+			ibrs_inuse ? "IBRS" : "retpoline");
 		return -EINVAL;
 	}
 
@@ -184,6 +193,8 @@ static ssize_t lfence_enabled_write(struct file *file,
 	else
 		clear_lfence_disabled();
 
+	refresh_set_spectre_v2_enabled();
+
 	mutex_unlock(&spec_ctrl_mutex);
 	return count;
 }