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Commit 288d152c authored by Nicolai Stange's avatar Nicolai Stange Committed by Thomas Gleixner
Browse files

x86/KVM/VMX: Initialize the vmx_l1d_flush_pages' content 



The slow path in vmx_l1d_flush() reads from vmx_l1d_flush_pages in order
to evict the L1d cache.

However, these pages are never cleared and, in theory, their data could be
leaked.

More importantly, KSM could merge a nested hypervisor's vmx_l1d_flush_pages
to fewer than 1 << L1D_CACHE_ORDER host physical pages and this would break
the L1d flushing algorithm: L1D on x86_64 is tagged by physical addresses.

Fix this by initializing the individual vmx_l1d_flush_pages with a
different pattern each.

Rename the "empty_zp" asm constraint identifier in vmx_l1d_flush() to
"flush_pages" to reflect this change.

Fixes: a47dd5f0 ("x86/KVM/VMX: Add L1D flush algorithm")
Signed-off-by: default avatarNicolai Stange <nstange@suse.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 6c26fcd2

arch/x86/kvm/vmx.c

+14 −3
Original line number Diff line number Diff line
@@ -211,6 +211,7 @@ static void *vmx_l1d_flush_pages; 
static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)

{

	struct page *page;

	unsigned int i;



	if (!enable_ept) {

		l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_EPT_DISABLED;
@@ -243,6 +244,16 @@ static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf) 
		if (!page)

			return -ENOMEM;

		vmx_l1d_flush_pages = page_address(page);



		/*

		 * Initialize each page with a different pattern in

		 * order to protect against KSM in the nested

		 * virtualization case.

		 */

		for (i = 0; i < 1u << L1D_CACHE_ORDER; ++i) {

			memset(vmx_l1d_flush_pages + i * PAGE_SIZE, i + 1,

			       PAGE_SIZE);

		}

	}



	l1tf_vmx_mitigation = l1tf;
@@ -9701,7 +9712,7 @@ static void vmx_l1d_flush(struct kvm_vcpu *vcpu) 
		/* First ensure the pages are in the TLB */

		"xorl	%%eax, %%eax\n"

		".Lpopulate_tlb:\n\t"

		"movzbl	(%[empty_zp], %%" _ASM_AX "), %%ecx\n\t"

		"movzbl	(%[flush_pages], %%" _ASM_AX "), %%ecx\n\t"

		"addl	$4096, %%eax\n\t"

		"cmpl	%%eax, %[size]\n\t"

		"jne	.Lpopulate_tlb\n\t"
@@ -9710,12 +9721,12 @@ static void vmx_l1d_flush(struct kvm_vcpu *vcpu) 
		/* Now fill the cache */

		"xorl	%%eax, %%eax\n"

		".Lfill_cache:\n"

		"movzbl	(%[empty_zp], %%" _ASM_AX "), %%ecx\n\t"

		"movzbl	(%[flush_pages], %%" _ASM_AX "), %%ecx\n\t"

		"addl	$64, %%eax\n\t"

		"cmpl	%%eax, %[size]\n\t"

		"jne	.Lfill_cache\n\t"

		"lfence\n"

		:: [empty_zp] "r" (vmx_l1d_flush_pages),

		:: [flush_pages] "r" (vmx_l1d_flush_pages),

		    [size] "r" (size)

		: "eax", "ebx", "ecx", "edx");

}