4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Nicolai Stange <nstange@xxxxxxx>
commit 288d152c23dcf3c09da46c5c481903ca10ebfef7 upstream
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: a47dd5f06714 ("x86/KVM/VMX: Add L1D flush algorithm")
Signed-off-by: Nicolai Stange <nstange@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/vmx.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -212,6 +212,7 @@ 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;
@@ -244,6 +245,16 @@ static int vmx_setup_l1d_flush(enum vmx_
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;
@@ -8675,7 +8686,7 @@ static void vmx_l1d_flush(struct kvm_vcp
/* 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"
@@ -8684,12 +8695,12 @@ static void vmx_l1d_flush(struct kvm_vcp
/* 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");
}
