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Commit 28a1f3ac authored by Junaid Shahid's avatar Junaid Shahid Committed by Paolo Bonzini
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kvm: x86: Set highest physical address bits in non-present/reserved SPTEs 



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: default avatarJunaid Shahid <junaids@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent fd8ca6da

arch/x86/kvm/mmu.c

+38 −5
Original line number Diff line number Diff line
@@ -238,6 +238,17 @@ static const u64 shadow_acc_track_saved_bits_mask = PT64_EPT_READABLE_MASK | 
						    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);

static union kvm_mmu_page_role

kvm_mmu_calc_root_page_role(struct kvm_vcpu *vcpu);
@@ -327,9 +338,13 @@ static void mark_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, u64 gfn, 
{

	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);
@@ -342,8 +357,14 @@ 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)
@@ -400,7 +421,7 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_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;
@@ -410,6 +431,18 @@ static void kvm_mmu_clear_all_pte_masks(void) 
	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)
@@ -5819,7 +5852,7 @@ 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),

arch/x86/kvm/x86.c

+6 −2
Original line number Diff line number Diff line
@@ -6536,8 +6536,12 @@ 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;