--- /dev/null
+From a629df7eadffb03e6ce4a8616e62ea29fdf69b6b Mon Sep 17 00:00:00 2001
+From: Paolo Bonzini <pbonzini@redhat.com>
+Date: Mon, 22 Dec 2014 10:43:39 +0100
+Subject: kvm: x86: drop severity of "generation wraparound" message
+
+From: Paolo Bonzini <pbonzini@redhat.com>
+
+commit a629df7eadffb03e6ce4a8616e62ea29fdf69b6b upstream.
+
+Since most virtual machines raise this message once, it is a bit annoying.
+Make it KERN_DEBUG severity.
+
+Fixes: 7a2e8aaf0f6873b47bc2347f216ea5b0e4c258ab
+Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ arch/x86/kvm/mmu.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+--- a/arch/x86/kvm/mmu.c
++++ b/arch/x86/kvm/mmu.c
+@@ -4384,7 +4384,7 @@ void kvm_mmu_invalidate_mmio_sptes(struc
+ * zap all shadow pages.
+ */
+ if (unlikely(kvm_current_mmio_generation(kvm) == 0)) {
+- printk_ratelimited(KERN_INFO "kvm: zapping shadow pages for mmio generation wraparound\n");
++ printk_ratelimited(KERN_DEBUG "kvm: zapping shadow pages for mmio generation wraparound\n");
+ kvm_mmu_invalidate_zap_all_pages(kvm);
+ }
+ }
--- /dev/null
+From 394f56fe480140877304d342dec46d50dc823d46 Mon Sep 17 00:00:00 2001
+From: Andy Lutomirski <luto@amacapital.net>
+Date: Fri, 19 Dec 2014 16:04:11 -0800
+Subject: x86_64, vdso: Fix the vdso address randomization algorithm
+
+From: Andy Lutomirski <luto@amacapital.net>
+
+commit 394f56fe480140877304d342dec46d50dc823d46 upstream.
+
+The theory behind vdso randomization is that it's mapped at a random
+offset above the top of the stack. To avoid wasting a page of
+memory for an extra page table, the vdso isn't supposed to extend
+past the lowest PMD into which it can fit. Other than that, the
+address should be a uniformly distributed address that meets all of
+the alignment requirements.
+
+The current algorithm is buggy: the vdso has about a 50% probability
+of being at the very end of a PMD. The current algorithm also has a
+decent chance of failing outright due to incorrect handling of the
+case where the top of the stack is near the top of its PMD.
+
+This fixes the implementation. The paxtest estimate of vdso
+"randomisation" improves from 11 bits to 18 bits. (Disclaimer: I
+don't know what the paxtest code is actually calculating.)
+
+It's worth noting that this algorithm is inherently biased: the vdso
+is more likely to end up near the end of its PMD than near the
+beginning. Ideally we would either nix the PMD sharing requirement
+or jointly randomize the vdso and the stack to reduce the bias.
+
+In the mean time, this is a considerable improvement with basically
+no risk of compatibility issues, since the allowed outputs of the
+algorithm are unchanged.
+
+As an easy test, doing this:
+
+for i in `seq 10000`
+ do grep -P vdso /proc/self/maps |cut -d- -f1
+done |sort |uniq -d
+
+used to produce lots of output (1445 lines on my most recent run).
+A tiny subset looks like this:
+
+7fffdfffe000
+7fffe01fe000
+7fffe05fe000
+7fffe07fe000
+7fffe09fe000
+7fffe0bfe000
+7fffe0dfe000
+
+Note the suspicious fe000 endings. With the fix, I get a much more
+palatable 76 repeated addresses.
+
+Reviewed-by: Kees Cook <keescook@chromium.org>
+Signed-off-by: Andy Lutomirski <luto@amacapital.net>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ arch/x86/vdso/vma.c | 43 +++++++++++++++++++++++++++++--------------
+ 1 file changed, 29 insertions(+), 14 deletions(-)
+
+--- a/arch/x86/vdso/vma.c
++++ b/arch/x86/vdso/vma.c
+@@ -117,30 +117,45 @@ subsys_initcall(init_vdso);
+
+ struct linux_binprm;
+
+-/* Put the vdso above the (randomized) stack with another randomized offset.
+- This way there is no hole in the middle of address space.
+- To save memory make sure it is still in the same PTE as the stack top.
+- This doesn't give that many random bits */
++/*
++ * Put the vdso above the (randomized) stack with another randomized
++ * offset. This way there is no hole in the middle of address space.
++ * To save memory make sure it is still in the same PTE as the stack
++ * top. This doesn't give that many random bits.
++ *
++ * Note that this algorithm is imperfect: the distribution of the vdso
++ * start address within a PMD is biased toward the end.
++ *
++ * Only used for the 64-bit and x32 vdsos.
++ */
+ static unsigned long vdso_addr(unsigned long start, unsigned len)
+ {
+ unsigned long addr, end;
+ unsigned offset;
+- end = (start + PMD_SIZE - 1) & PMD_MASK;
++
++ /*
++ * Round up the start address. It can start out unaligned as a result
++ * of stack start randomization.
++ */
++ start = PAGE_ALIGN(start);
++
++ /* Round the lowest possible end address up to a PMD boundary. */
++ end = (start + len + PMD_SIZE - 1) & PMD_MASK;
+ if (end >= TASK_SIZE_MAX)
+ end = TASK_SIZE_MAX;
+ end -= len;
+- /* This loses some more bits than a modulo, but is cheaper */
+- offset = get_random_int() & (PTRS_PER_PTE - 1);
+- addr = start + (offset << PAGE_SHIFT);
+- if (addr >= end)
+- addr = end;
++
++ if (end > start) {
++ offset = get_random_int() % (((end - start) >> PAGE_SHIFT) + 1);
++ addr = start + (offset << PAGE_SHIFT);
++ } else {
++ addr = start;
++ }
+
+ /*
+- * page-align it here so that get_unmapped_area doesn't
+- * align it wrongfully again to the next page. addr can come in 4K
+- * unaligned here as a result of stack start randomization.
++ * Forcibly align the final address in case we have a hardware
++ * issue that requires alignment for performance reasons.
+ */
+- addr = PAGE_ALIGN(addr);
+ addr = align_vdso_addr(addr);
+
+ return addr;
projects / thirdparty / kernel / stable-queue.git / commitdiff
