4.18-stable review patch. If anyone has any objections, please let me know.
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From: Junaid Shahid junaids@google.com
commit 28a1f3ac1d0c8558ee4453d9634dad891a6e922e upstream.
Always set the 5 upper-most supported physical address bits to 1 for SPTEs that are marked as non-present or reserved, to make them unusable for L1TF attacks from the guest. Currently, this just applies to MMIO SPTEs. (We do not need to mark PTEs that are completely 0 as physical page 0 is already reserved.)
This allows mitigation of L1TF without disabling hyper-threading by using shadow paging mode instead of EPT.
Signed-off-by: Junaid Shahid junaids@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kvm/mmu.c | 43 ++++++++++++++++++++++++++++++++++++++----- arch/x86/kvm/x86.c | 8 ++++++-- 2 files changed, 44 insertions(+), 7 deletions(-)
--- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -221,6 +221,17 @@ static const u64 shadow_acc_track_saved_ PT64_EPT_EXECUTABLE_MASK; static const u64 shadow_acc_track_saved_bits_shift = PT64_SECOND_AVAIL_BITS_SHIFT;
+/* + * This mask must be set on all non-zero Non-Present or Reserved SPTEs in order + * to guard against L1TF attacks. + */ +static u64 __read_mostly shadow_nonpresent_or_rsvd_mask; + +/* + * The number of high-order 1 bits to use in the mask above. + */ +static const u64 shadow_nonpresent_or_rsvd_mask_len = 5; + static void mmu_spte_set(u64 *sptep, u64 spte);
void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask, u64 mmio_value) @@ -308,9 +319,13 @@ static void mark_mmio_spte(struct kvm_vc { unsigned int gen = kvm_current_mmio_generation(vcpu); u64 mask = generation_mmio_spte_mask(gen); + u64 gpa = gfn << PAGE_SHIFT;
access &= ACC_WRITE_MASK | ACC_USER_MASK; - mask |= shadow_mmio_value | access | gfn << PAGE_SHIFT; + mask |= shadow_mmio_value | access; + mask |= gpa | shadow_nonpresent_or_rsvd_mask; + mask |= (gpa & shadow_nonpresent_or_rsvd_mask) + << shadow_nonpresent_or_rsvd_mask_len;
trace_mark_mmio_spte(sptep, gfn, access, gen); mmu_spte_set(sptep, mask); @@ -323,8 +338,14 @@ static bool is_mmio_spte(u64 spte)
static gfn_t get_mmio_spte_gfn(u64 spte) { - u64 mask = generation_mmio_spte_mask(MMIO_GEN_MASK) | shadow_mmio_mask; - return (spte & ~mask) >> PAGE_SHIFT; + u64 mask = generation_mmio_spte_mask(MMIO_GEN_MASK) | shadow_mmio_mask | + shadow_nonpresent_or_rsvd_mask; + u64 gpa = spte & ~mask; + + gpa |= (spte >> shadow_nonpresent_or_rsvd_mask_len) + & shadow_nonpresent_or_rsvd_mask; + + return gpa >> PAGE_SHIFT; }
static unsigned get_mmio_spte_access(u64 spte) @@ -381,7 +402,7 @@ void kvm_mmu_set_mask_ptes(u64 user_mask } EXPORT_SYMBOL_GPL(kvm_mmu_set_mask_ptes);
-static void kvm_mmu_clear_all_pte_masks(void) +static void kvm_mmu_reset_all_pte_masks(void) { shadow_user_mask = 0; shadow_accessed_mask = 0; @@ -391,6 +412,18 @@ static void kvm_mmu_clear_all_pte_masks( shadow_mmio_mask = 0; shadow_present_mask = 0; shadow_acc_track_mask = 0; + + /* + * If the CPU has 46 or less physical address bits, then set an + * appropriate mask to guard against L1TF attacks. Otherwise, it is + * assumed that the CPU is not vulnerable to L1TF. + */ + if (boot_cpu_data.x86_phys_bits < + 52 - shadow_nonpresent_or_rsvd_mask_len) + shadow_nonpresent_or_rsvd_mask = + rsvd_bits(boot_cpu_data.x86_phys_bits - + shadow_nonpresent_or_rsvd_mask_len, + boot_cpu_data.x86_phys_bits - 1); }
static int is_cpuid_PSE36(void) @@ -5500,7 +5533,7 @@ int kvm_mmu_module_init(void) { int ret = -ENOMEM;
- kvm_mmu_clear_all_pte_masks(); + kvm_mmu_reset_all_pte_masks();
pte_list_desc_cache = kmem_cache_create("pte_list_desc", sizeof(struct pte_list_desc), --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6506,8 +6506,12 @@ static void kvm_set_mmio_spte_mask(void) * Set the reserved bits and the present bit of an paging-structure * entry to generate page fault with PFER.RSV = 1. */ - /* Mask the reserved physical address bits. */ - mask = rsvd_bits(maxphyaddr, 51); + + /* + * Mask the uppermost physical address bit, which would be reserved as + * long as the supported physical address width is less than 52. + */ + mask = 1ull << 51;
/* Set the present bit. */ mask |= 1ull;