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Message-ID: <20200402152340.GL20713@hirez.programming.kicks-ass.net>
Date: Thu, 2 Apr 2020 17:23:40 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
"Kenneth R. Crudup" <kenny@...ix.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Jessica Yu <jeyu@...nel.org>,
Fenghua Yu <fenghua.yu@...el.com>,
Xiaoyao Li <xiaoyao.li@...el.com>,
Nadav Amit <namit@...are.com>,
Thomas Hellstrom <thellstrom@...are.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Tony Luck <tony.luck@...el.com>,
Steven Rostedt <rostedt@...dmis.org>
Subject: [patch v2 1/2] x86,module: Detect VMX modules and disable
Split-Lock-Detect
I picked VMXOFF (which also appears in vmmon.ko) instead of VMXON
because that latter takes an argument is therefore more difficult to
decode.
---
Subject: x86,module: Detect VMX modules and disable Split-Lock-Detect
From: Peter Zijlstra <peterz@...radead.org>
Date: Thu, 02 Apr 2020 14:32:59 +0200
It turns out that with Split-Lock-Detect enabled (default) any VMX
hypervisor needs at least a little modification in order to not blindly
inject the #AC into the guest without the guest being ready for it.
Since there is no telling which module implements a hypervisor, scan the
module text and look for the VMLAUNCH/VMXOFF instructions. If found, the
module is assumed to be a hypervisor of some sort and SLD is disabled.
Hypervisors, which have been modified and are known to work correctly,
can add:
MODULE_INFO(sld_safe, "Y");
to explicitly tell the module loader they're good.
NOTE: it is unfortunate that struct load_info is not available to the
arch module code, this means CONFIG_CPU_SUP_INTEL gunk is needed
in generic code.
NOTE: while we can 'trivially' fix KVM, we're still stuck with stuff
like VMware and VirtualBox doing their own thing.
Reported-by: "Kenneth R. Crudup" <kenny@...ix.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
arch/x86/include/asm/cpu.h | 2 ++
arch/x86/kernel/cpu/intel.c | 41 ++++++++++++++++++++++++++++++++++++++++-
arch/x86/kernel/module.c | 6 ++++++
include/linux/module.h | 4 ++++
kernel/module.c | 5 +++++
5 files changed, 57 insertions(+), 1 deletion(-)
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -44,6 +44,7 @@ unsigned int x86_stepping(unsigned int s
extern void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c);
extern void switch_to_sld(unsigned long tifn);
extern bool handle_user_split_lock(struct pt_regs *regs, long error_code);
+extern void split_lock_validate_module_text(struct module *me, void *text, void *text_end);
#else
static inline void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c) {}
static inline void switch_to_sld(unsigned long tifn) {}
@@ -51,5 +52,6 @@ static inline bool handle_user_split_loc
{
return false;
}
+static inline void split_lock_validate_module_text(struct module *me, void *text, void *text_end) {}
#endif
#endif /* _ASM_X86_CPU_H */
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -9,6 +9,7 @@
#include <linux/thread_info.h>
#include <linux/init.h>
#include <linux/uaccess.h>
+#include <linux/module.h>
#include <asm/cpufeature.h>
#include <asm/pgtable.h>
@@ -21,6 +22,7 @@
#include <asm/elf.h>
#include <asm/cpu_device_id.h>
#include <asm/cmdline.h>
+#include <asm/insn.h>
#ifdef CONFIG_X86_64
#include <linux/topology.h>
@@ -1055,12 +1057,49 @@ static void sld_update_msr(bool on)
{
u64 test_ctrl_val = msr_test_ctrl_cache;
- if (on)
+ if (on && (sld_state != sld_off))
test_ctrl_val |= MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
wrmsrl(MSR_TEST_CTRL, test_ctrl_val);
}
+static void sld_remote_kill(void *arg)
+{
+ sld_update_msr(false);
+}
+
+void split_lock_validate_module_text(struct module *me, void *text, void *text_end)
+{
+ u8 vmxoff[] = { 0x0f, 0x01, 0xc4 };
+ u8 vmlaunch[] = { 0x0f, 0x01, 0xc2 };
+ struct insn insn;
+
+ if (sld_state == sld_off)
+ return;
+
+ while (text < text_end) {
+ kernel_insn_init(&insn, text, text_end - text);
+ insn_get_length(&insn);
+
+ if (WARN_ON_ONCE(!insn_complete(&insn)))
+ break;
+
+ if (insn.length == 3 &&
+ (!memcmp(text, vmlaunch, sizeof(vmlaunch)) ||
+ !memcmp(text, vmxoff, sizeof(vmxoff))))
+ goto bad_module;
+
+ text += insn.length;
+ }
+
+ return;
+
+bad_module:
+ pr_warn("disabled due to VMX in module: %s\n", me->name);
+ sld_state = sld_off;
+ on_each_cpu(sld_remote_kill, NULL, 1);
+}
+
static void split_lock_init(void)
{
split_lock_verify_msr(sld_state != sld_off);
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -24,6 +24,7 @@
#include <asm/pgtable.h>
#include <asm/setup.h>
#include <asm/unwind.h>
+#include <asm/cpu.h>
#if 0
#define DEBUGP(fmt, ...) \
@@ -253,6 +254,11 @@ int module_finalize(const Elf_Ehdr *hdr,
tseg, tseg + text->sh_size);
}
+ if (text && !me->sld_safe) {
+ void *tseg = (void *)text->sh_addr;
+ split_lock_validate_module_text(me, tseg, tseg + text->sh_size);
+ }
+
if (para) {
void *pseg = (void *)para->sh_addr;
apply_paravirt(pseg, pseg + para->sh_size);
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -407,6 +407,10 @@ struct module {
bool sig_ok;
#endif
+#ifdef CONFIG_CPU_SUP_INTEL
+ bool sld_safe;
+#endif
+
bool async_probe_requested;
/* symbols that will be GPL-only in the near future. */
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3096,6 +3096,11 @@ static int check_modinfo(struct module *
"is unknown, you have been warned.\n", mod->name);
}
+#ifdef CONFIG_CPU_SUP_INTEL
+ if (get_modinfo(info, "sld_safe"))
+ mod->sld_safe = true;
+#endif
+
err = check_modinfo_livepatch(mod, info);
if (err)
return err;
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