4.18-stable review patch. If anyone has any objections, please let me know.
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From: Nicolai Stange nstange@suse.de
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@suse.de Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 @@ -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_ 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; @@ -9737,7 +9748,7 @@ 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" @@ -9746,12 +9757,12 @@ 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"); }