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Date: Wed, 5 Oct 2022 13:31:57 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Alexandre Chartre <alexandre.chartre@...cle.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Borislav Petkov <bp@...e.de>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Subject: [PATCH 5.4 09/51] x86/bugs: Add AMD retbleed= boot parameter
From: Alexandre Chartre <alexandre.chartre@...cle.com>
commit 7fbf47c7ce50b38a64576b150e7011ae73d54669 upstream.
Add the "retbleed=<value>" boot parameter to select a mitigation for
RETBleed. Possible values are "off", "auto" and "unret"
(JMP2RET mitigation). The default value is "auto".
Currently, "retbleed=auto" will select the unret mitigation on
AMD and Hygon and no mitigation on Intel (JMP2RET is not effective on
Intel).
[peterz: rebase; add hygon]
[jpoimboe: cleanups]
Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
[cascardo: this effectively remove the UNRET mitigation as an option, so it
has to be complemented by a later pick of the same commit later. This is
done in order to pick retbleed_select_mitigation]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
Documentation/admin-guide/kernel-parameters.txt | 12 +++
arch/x86/kernel/cpu/bugs.c | 74 +++++++++++++++++++++++-
2 files changed, 85 insertions(+), 1 deletion(-)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4298,6 +4298,18 @@
retain_initrd [RAM] Keep initrd memory after extraction
+ retbleed= [X86] Control mitigation of RETBleed (Arbitrary
+ Speculative Code Execution with Return Instructions)
+ vulnerability.
+
+ off - unconditionally disable
+ auto - automatically select a migitation
+
+ Selecting 'auto' will choose a mitigation method at run
+ time according to the CPU.
+
+ Not specifying this option is equivalent to retbleed=auto.
+
rfkill.default_state=
0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
etc. communication is blocked by default.
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -36,6 +36,7 @@
#include "cpu.h"
static void __init spectre_v1_select_mitigation(void);
+static void __init retbleed_select_mitigation(void);
static void __init spectre_v2_select_mitigation(void);
static void __init ssb_select_mitigation(void);
static void __init l1tf_select_mitigation(void);
@@ -111,6 +112,12 @@ void __init check_bugs(void)
/* Select the proper CPU mitigations before patching alternatives: */
spectre_v1_select_mitigation();
+ retbleed_select_mitigation();
+ /*
+ * spectre_v2_select_mitigation() relies on the state set by
+ * retbleed_select_mitigation(); specifically the STIBP selection is
+ * forced for UNRET.
+ */
spectre_v2_select_mitigation();
ssb_select_mitigation();
l1tf_select_mitigation();
@@ -706,6 +713,71 @@ static int __init nospectre_v1_cmdline(c
early_param("nospectre_v1", nospectre_v1_cmdline);
#undef pr_fmt
+#define pr_fmt(fmt) "RETBleed: " fmt
+
+enum retbleed_mitigation {
+ RETBLEED_MITIGATION_NONE,
+};
+
+enum retbleed_mitigation_cmd {
+ RETBLEED_CMD_OFF,
+ RETBLEED_CMD_AUTO,
+};
+
+const char * const retbleed_strings[] = {
+ [RETBLEED_MITIGATION_NONE] = "Vulnerable",
+};
+
+static enum retbleed_mitigation retbleed_mitigation __ro_after_init =
+ RETBLEED_MITIGATION_NONE;
+static enum retbleed_mitigation_cmd retbleed_cmd __ro_after_init =
+ RETBLEED_CMD_AUTO;
+
+static int __init retbleed_parse_cmdline(char *str)
+{
+ if (!str)
+ return -EINVAL;
+
+ if (!strcmp(str, "off"))
+ retbleed_cmd = RETBLEED_CMD_OFF;
+ else if (!strcmp(str, "auto"))
+ retbleed_cmd = RETBLEED_CMD_AUTO;
+ else
+ pr_err("Unknown retbleed option (%s). Defaulting to 'auto'\n", str);
+
+ return 0;
+}
+early_param("retbleed", retbleed_parse_cmdline);
+
+#define RETBLEED_UNTRAIN_MSG "WARNING: BTB untrained return thunk mitigation is only effective on AMD/Hygon!\n"
+#define RETBLEED_COMPILER_MSG "WARNING: kernel not compiled with RETPOLINE or -mfunction-return capable compiler!\n"
+
+static void __init retbleed_select_mitigation(void)
+{
+ if (!boot_cpu_has_bug(X86_BUG_RETBLEED) || cpu_mitigations_off())
+ return;
+
+ switch (retbleed_cmd) {
+ case RETBLEED_CMD_OFF:
+ return;
+
+ case RETBLEED_CMD_AUTO:
+ default:
+ if (!boot_cpu_has_bug(X86_BUG_RETBLEED))
+ break;
+
+ break;
+ }
+
+ switch (retbleed_mitigation) {
+ default:
+ break;
+ }
+
+ pr_info("%s\n", retbleed_strings[retbleed_mitigation]);
+}
+
+#undef pr_fmt
#define pr_fmt(fmt) "Spectre V2 : " fmt
static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init =
@@ -1913,7 +1985,7 @@ static ssize_t srbds_show_state(char *bu
static ssize_t retbleed_show_state(char *buf)
{
- return sprintf(buf, "Vulnerable\n");
+ return sprintf(buf, "%s\n", retbleed_strings[retbleed_mitigation]);
}
static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
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