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Message-ID: <725ca48f-8194-658e-0296-65d4368803b5@intel.com>
Date: Fri, 3 Apr 2020 00:20:08 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Peter Zijlstra <peterz@...radead.org>,
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>,
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: Re: [patch v2 1/2] x86,module: Detect VMX modules and disable
Split-Lock-Detect
On 4/2/2020 11:23 PM, Peter Zijlstra wrote:
>
> 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;
shouldn't we remove the __ro_after_init of sld_state?
And, shouldn't we clear X86_FEATURE_SPLIT_LOCK_DETECT flag?
> + 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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