Messages in this thread Patch in this message |  | | Date | Thu, 2 Apr 2020 17:23:40 +0200 | From | Peter Zijlstra <> | Subject | [patch v2 1/2] x86,module: Detect VMX modules and disable Split-Lock-Detect |
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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; + 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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