Messages in this thread | | | Date | Tue, 10 Jan 2023 13:06:38 -0600 | Subject | Re: [PATCH kernel v2 2/3] KVM: SEV: Enable data breakpoints in SEV-ES | From | Tom Lendacky <> |
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On 1/10/23 12:00, Borislav Petkov wrote: > On Fri, Dec 09, 2022 at 03:38:03PM +1100, Alexey Kardashevskiy wrote: >>
>> "DR7 access must remain intercepted for an SEV-ES guest" - I could not >> figure out the exact reasoning why it is there in the first place, >> IIUC this is to prevent loop of #DBs in the VM. > > Let's ask Mr. Lendacky: > > 8d4846b9b150 ("KVM: SVM: Prevent debugging under SEV-ES")
The DR7 requirements were to prevent a malicious SEV-ES guest from setting up data breakpoints on the #VC IDT entry/stack and causing an infinite loop.
Thanks, Tom
> >> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c >> index efaaef2b7ae1..800ea2a778cc 100644 >> --- a/arch/x86/kvm/svm/sev.c >> +++ b/arch/x86/kvm/svm/sev.c >> @@ -21,6 +21,7 @@ >> #include <asm/pkru.h> >> #include <asm/trapnr.h> >> #include <asm/fpu/xcr.h> >> +#include <asm/debugreg.h> >> >> #include "mmu.h" >> #include "x86.h" >> @@ -52,11 +53,21 @@ module_param_named(sev, sev_enabled, bool, 0444); >> /* enable/disable SEV-ES support */ >> static bool sev_es_enabled = true; >> module_param_named(sev_es, sev_es_enabled, bool, 0444); >> + >> +/* enable/disable SEV-ES DebugSwap support */ >> +static bool sev_es_debug_swap_enabled = true; >> +module_param_named(debug_swap, sev_es_debug_swap_enabled, bool, 0644); >> #else >> #define sev_enabled false >> #define sev_es_enabled false >> +#define sev_es_debug_swap false >> #endif /* CONFIG_KVM_AMD_SEV */ >> >> +bool sev_es_is_debug_swap_enabled(void) >> +{ >> + return sev_es_debug_swap_enabled; >> +} >> + >> static u8 sev_enc_bit; >> static DECLARE_RWSEM(sev_deactivate_lock); >> static DEFINE_MUTEX(sev_bitmap_lock); >> @@ -604,6 +615,9 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm) >> save->xss = svm->vcpu.arch.ia32_xss; >> save->dr6 = svm->vcpu.arch.dr6; >> >> + if (sev_es_is_debug_swap_enabled()) >> + save->sev_features |= SVM_SEV_FEAT_DEBUG_SWAP; >> + >> pr_debug("Virtual Machine Save Area (VMSA):\n"); >> print_hex_dump_debug("", DUMP_PREFIX_NONE, 16, 1, save, sizeof(*save), false); >> >> @@ -2249,6 +2263,9 @@ void __init sev_hardware_setup(void) >> out: >> sev_enabled = sev_supported; >> sev_es_enabled = sev_es_supported; >> + if (sev_es_debug_swap_enabled) >> + sev_es_debug_swap_enabled = sev_es_enabled && >> + boot_cpu_has(X86_FEATURE_NO_NESTED_DATA_BP); > > check_for_deprecated_apis: WARNING: arch/x86/kvm/svm/sev.c:2268: Do not use boot_cpu_has() - use cpu_feature_enabled() instead. >
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