Messages in this thread |  | | Subject | Re: [patch v2 1/2] x86,module: Detect VMX modules and disable Split-Lock-Detect | From | Xiaoyao Li <> | Date | Fri, 3 Apr 2020 00:20:08 +0800 |
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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@infradead.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@panix.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.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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