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Message-ID: <lsq.1520823972.121191571@decadent.org.uk>
Date: Mon, 12 Mar 2018 03:06:12 +0000
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC: akpm@...ux-foundation.org, "Andi Kleen" <ak@...ux.intel.com>,
torvalds@...ux-foundation.org, arjan@...ux.intel.com,
jeyu@...nel.org, gregkh@...uxfoundation.org,
"David Woodhouse" <dwmw2@...radead.org>,
"Thomas Gleixner" <tglx@...utronix.de>
Subject: [PATCH 3.16 46/76] module/retpoline: Warn about missing retpoline
in module
3.16.56-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Andi Kleen <ak@...ux.intel.com>
commit caf7501a1b4ec964190f31f9c3f163de252273b8 upstream.
There's a risk that a kernel which has full retpoline mitigations becomes
vulnerable when a module gets loaded that hasn't been compiled with the
right compiler or the right option.
To enable detection of that mismatch at module load time, add a module info
string "retpoline" at build time when the module was compiled with
retpoline support. This only covers compiled C source, but assembler source
or prebuilt object files are not checked.
If a retpoline enabled kernel detects a non retpoline protected module at
load time, print a warning and report it in the sysfs vulnerability file.
[ tglx: Massaged changelog ]
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: gregkh@...uxfoundation.org
Cc: torvalds@...ux-foundation.org
Cc: jeyu@...nel.org
Cc: arjan@...ux.intel.com
Link: https://lkml.kernel.org/r/20180125235028.31211-1-andi@firstfloor.org
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
arch/x86/kernel/cpu/bugs.c | 17 ++++++++++++++++-
include/linux/module.h | 9 +++++++++
kernel/module.c | 11 +++++++++++
scripts/mod/modpost.c | 9 +++++++++
4 files changed, 45 insertions(+), 1 deletion(-)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -10,6 +10,7 @@
#include <linux/init.h>
#include <linux/utsname.h>
#include <linux/cpu.h>
+#include <linux/module.h>
#include <asm/nospec-branch.h>
#include <asm/cmdline.h>
@@ -155,6 +156,19 @@ static const char *spectre_v2_strings[]
#define pr_fmt(fmt) "Spectre V2 mitigation: " fmt
static enum spectre_v2_mitigation spectre_v2_enabled = SPECTRE_V2_NONE;
+static bool spectre_v2_bad_module;
+
+#ifdef RETPOLINE
+bool retpoline_module_ok(bool has_retpoline)
+{
+ if (spectre_v2_enabled == SPECTRE_V2_NONE || has_retpoline)
+ return true;
+
+ pr_err("System may be vunerable to spectre v2\n");
+ spectre_v2_bad_module = true;
+ return false;
+}
+#endif
static void __init spec2_print_if_insecure(const char *reason)
{
@@ -340,6 +354,7 @@ ssize_t cpu_show_spectre_v2(struct devic
if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
return sprintf(buf, "Not affected\n");
- return sprintf(buf, "%s\n", spectre_v2_strings[spectre_v2_enabled]);
+ return sprintf(buf, "%s%s\n", spectre_v2_strings[spectre_v2_enabled],
+ spectre_v2_bad_module ? " - vulnerable module loaded" : "");
}
#endif
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -656,4 +656,13 @@ static inline void module_bug_finalize(c
static inline void module_bug_cleanup(struct module *mod) {}
#endif /* CONFIG_GENERIC_BUG */
+#ifdef RETPOLINE
+extern bool retpoline_module_ok(bool has_retpoline);
+#else
+static inline bool retpoline_module_ok(bool has_retpoline)
+{
+ return true;
+}
+#endif
+
#endif /* _LINUX_MODULE_H */
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2494,6 +2494,15 @@ static int elf_header_check(struct load_
return 0;
}
+static void check_modinfo_retpoline(struct module *mod, struct load_info *info)
+{
+ if (retpoline_module_ok(get_modinfo(info, "retpoline")))
+ return;
+
+ pr_warn("%s: loading module not compiled with retpoline compiler.\n",
+ mod->name);
+}
+
/* Sets info->hdr and info->len. */
static int copy_module_from_user(const void __user *umod, unsigned long len,
struct load_info *info)
@@ -2698,6 +2707,8 @@ static int check_modinfo(struct module *
if (!get_modinfo(info, "intree"))
add_taint_module(mod, TAINT_OOT_MODULE, LOCKDEP_STILL_OK);
+ check_modinfo_retpoline(mod, info);
+
if (get_modinfo(info, "staging")) {
add_taint_module(mod, TAINT_CRAP, LOCKDEP_STILL_OK);
pr_warn("%s: module is from the staging directory, the quality "
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1952,6 +1952,14 @@ static void add_intree_flag(struct buffe
buf_printf(b, "\nMODULE_INFO(intree, \"Y\");\n");
}
+/* Cannot check for assembler */
+static void add_retpoline(struct buffer *b)
+{
+ buf_printf(b, "\n#ifdef RETPOLINE\n");
+ buf_printf(b, "MODULE_INFO(retpoline, \"Y\");\n");
+ buf_printf(b, "#endif\n");
+}
+
static void add_staging_flag(struct buffer *b, const char *name)
{
static const char *staging_dir = "drivers/staging";
@@ -2282,6 +2290,7 @@ int main(int argc, char **argv)
add_header(&buf, mod);
add_intree_flag(&buf, !external_module);
+ add_retpoline(&buf);
add_staging_flag(&buf, mod->name);
err |= add_versions(&buf, mod);
add_depends(&buf, mod, modules);
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