x86/srso: Add IBPB

Upstream commit: 233d6f68b98d480a7c42ebe78c38f79d44741ca9

Add the option to mitigate using IBPB on a kernel entry. Pull in the
Retbleed alternative so that the IBPB call from there can be used. Also,
if Retbleed mitigation is done using IBPB, the same mitigation can and
must be used here.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 25 insertions, 1 deletions

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 01e90e68f0c7..4a12dfdd317c 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -173,7 +173,8 @@
  * where we have a stack but before any RET instruction.
  */
 .macro UNTRAIN_RET
-#if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_IBPB_ENTRY)
+#if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_IBPB_ENTRY) || \
+	defined(CONFIG_CPU_SRSO)
 	ANNOTATE_UNRET_END
 	ALTERNATIVE_2 "",						\
 	              CALL_ZEN_UNTRAIN_RET, X86_FEATURE_UNRET,		\
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index ea7707b43d3f..fbb96bdfd8ba 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2315,18 +2315,21 @@ enum srso_mitigation {
 	SRSO_MITIGATION_NONE,
 	SRSO_MITIGATION_MICROCODE,
 	SRSO_MITIGATION_SAFE_RET,
+	SRSO_MITIGATION_IBPB,
 };
 
 enum srso_mitigation_cmd {
 	SRSO_CMD_OFF,
 	SRSO_CMD_MICROCODE,
 	SRSO_CMD_SAFE_RET,
+	SRSO_CMD_IBPB,
 };
 
 static const char * const srso_strings[] = {
 	[SRSO_MITIGATION_NONE]           = "Vulnerable",
 	[SRSO_MITIGATION_MICROCODE]      = "Mitigation: microcode",
 	[SRSO_MITIGATION_SAFE_RET]	 = "Mitigation: safe RET",
+	[SRSO_MITIGATION_IBPB]		 = "Mitigation: IBPB",
 };
 
 static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_NONE;
@@ -2343,6 +2346,8 @@ static int __init srso_parse_cmdline(char *str)
 		srso_cmd = SRSO_CMD_MICROCODE;
 	else if (!strcmp(str, "safe-ret"))
 		srso_cmd = SRSO_CMD_SAFE_RET;
+	else if (!strcmp(str, "ibpb"))
+		srso_cmd = SRSO_CMD_IBPB;
 	else
 		pr_err("Ignoring unknown SRSO option (%s).", str);
 
@@ -2384,6 +2389,14 @@ static void __init srso_select_mitigation(void)
 			setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
 	}
 
+	if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB) {
+		if (has_microcode) {
+			pr_err("Retbleed IBPB mitigation enabled, using same for SRSO\n");
+			srso_mitigation = SRSO_MITIGATION_IBPB;
+			goto pred_cmd;
+		}
+	}
+
 	switch (srso_cmd) {
 	case SRSO_CMD_OFF:
 		return;
@@ -2408,6 +2421,16 @@ static void __init srso_select_mitigation(void)
 		}
 		break;
 
+	case SRSO_CMD_IBPB:
+		if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
+			if (has_microcode) {
+				setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+				srso_mitigation = SRSO_MITIGATION_IBPB;
+			}
+		} else {
+			pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
+			goto pred_cmd;
+		}
 	default:
 		break;
 	}