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Commit bf998156 authored by Huang Ying's avatar Huang Ying Committed by Avi Kivity
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KVM: Avoid killing userspace through guest SRAO MCE on unmapped pages 



In common cases, guest SRAO MCE will cause corresponding poisoned page
be un-mapped and SIGBUS be sent to QEMU-KVM, then QEMU-KVM will relay
the MCE to guest OS.

But it is reported that if the poisoned page is accessed in guest
after unmapping and before MCE is relayed to guest OS, userspace will
be killed.

The reason is as follows. Because poisoned page has been un-mapped,
guest access will cause guest exit and kvm_mmu_page_fault will be
called. kvm_mmu_page_fault can not get the poisoned page for fault
address, so kernel and user space MMIO processing is tried in turn. In
user MMIO processing, poisoned page is accessed again, then userspace
is killed by force_sig_info.

To fix the bug, kvm_mmu_page_fault send HWPOISON signal to QEMU-KVM
and do not try kernel and user space MMIO processing for poisoned
page.

[xiao: fix warning introduced by avi]

Reported-by: default avatarMax Asbock <masbock@linux.vnet.ibm.com>
Signed-off-by: default avatarHuang Ying <ying.huang@intel.com>
Signed-off-by: default avatarXiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 540ad6b6

arch/x86/kvm/mmu.c

+26 −8
Original line number Diff line number Diff line
@@ -32,6 +32,7 @@ 
#include <linux/compiler.h>

#include <linux/srcu.h>

#include <linux/slab.h>

#include <linux/uaccess.h>



#include <asm/page.h>

#include <asm/cmpxchg.h>
@@ -1960,6 +1961,27 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write, 
	return pt_write;

}



static void kvm_send_hwpoison_signal(struct kvm *kvm, gfn_t gfn)

{

	char buf[1];

	void __user *hva;

	int r;



	/* Touch the page, so send SIGBUS */

	hva = (void __user *)gfn_to_hva(kvm, gfn);

	r = copy_from_user(buf, hva, 1);

}



static int kvm_handle_bad_page(struct kvm *kvm, gfn_t gfn, pfn_t pfn)

{

	kvm_release_pfn_clean(pfn);

	if (is_hwpoison_pfn(pfn)) {

		kvm_send_hwpoison_signal(kvm, gfn);

		return 0;

	}

	return 1;

}



static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)

{

	int r;
@@ -1983,10 +2005,8 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn) 
	pfn = gfn_to_pfn(vcpu->kvm, gfn);



	/* mmio */

	if (is_error_pfn(pfn)) {

		kvm_release_pfn_clean(pfn);

		return 1;

	}

	if (is_error_pfn(pfn))

		return kvm_handle_bad_page(vcpu->kvm, gfn, pfn);



	spin_lock(&vcpu->kvm->mmu_lock);

	if (mmu_notifier_retry(vcpu, mmu_seq))
@@ -2198,10 +2218,8 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, 
	mmu_seq = vcpu->kvm->mmu_notifier_seq;

	smp_rmb();

	pfn = gfn_to_pfn(vcpu->kvm, gfn);

	if (is_error_pfn(pfn)) {

		kvm_release_pfn_clean(pfn);

		return 1;

	}

	if (is_error_pfn(pfn))

		return kvm_handle_bad_page(vcpu->kvm, gfn, pfn);

	spin_lock(&vcpu->kvm->mmu_lock);

	if (mmu_notifier_retry(vcpu, mmu_seq))

		goto out_unlock;

arch/x86/kvm/paging_tmpl.h

+2 −5
Original line number Diff line number Diff line
@@ -431,11 +431,8 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, 
	pfn = gfn_to_pfn(vcpu->kvm, walker.gfn);



	/* mmio */

	if (is_error_pfn(pfn)) {

		pgprintk("gfn %lx is mmio\n", walker.gfn);

		kvm_release_pfn_clean(pfn);

		return 1;

	}

	if (is_error_pfn(pfn))

		return kvm_handle_bad_page(vcpu->kvm, walker.gfn, pfn);



	spin_lock(&vcpu->kvm->mmu_lock);

	if (mmu_notifier_retry(vcpu, mmu_seq))

include/linux/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -266,6 +266,7 @@ extern pfn_t bad_pfn; 


int is_error_page(struct page *page);

int is_error_pfn(pfn_t pfn);

int is_hwpoison_pfn(pfn_t pfn);

int kvm_is_error_hva(unsigned long addr);

int kvm_set_memory_region(struct kvm *kvm,

			  struct kvm_userspace_memory_region *mem,

include/linux/mm.h

+8 −0
Original line number Diff line number Diff line
@@ -1465,6 +1465,14 @@ extern int sysctl_memory_failure_recovery; 
extern void shake_page(struct page *p, int access);

extern atomic_long_t mce_bad_pages;

extern int soft_offline_page(struct page *page, int flags);

#ifdef CONFIG_MEMORY_FAILURE

int is_hwpoison_address(unsigned long addr);

#else

static inline int is_hwpoison_address(unsigned long addr)

{

	return 0;

}

#endif



extern void dump_page(struct page *page);

mm/memory-failure.c

+30 −0
Original line number Diff line number Diff line
@@ -45,6 +45,7 @@ 
#include <linux/page-isolation.h>

#include <linux/suspend.h>

#include <linux/slab.h>

#include <linux/swapops.h>

#include "internal.h"



int sysctl_memory_failure_early_kill __read_mostly = 0;
@@ -1296,3 +1297,32 @@ int soft_offline_page(struct page *page, int flags) 
	/* keep elevated page count for bad page */

	return ret;

}



int is_hwpoison_address(unsigned long addr)

{

	pgd_t *pgdp;

	pud_t pud, *pudp;

	pmd_t pmd, *pmdp;

	pte_t pte, *ptep;

	swp_entry_t entry;



	pgdp = pgd_offset(current->mm, addr);

	if (!pgd_present(*pgdp))

		return 0;

	pudp = pud_offset(pgdp, addr);

	pud = *pudp;

	if (!pud_present(pud) || pud_large(pud))

		return 0;

	pmdp = pmd_offset(pudp, addr);

	pmd = *pmdp;

	if (!pmd_present(pmd) || pmd_large(pmd))

		return 0;

	ptep = pte_offset_map(pmdp, addr);

	pte = *ptep;

	pte_unmap(ptep);

	if (!is_swap_pte(pte))

		return 0;

	entry = pte_to_swp_entry(pte);

	return is_hwpoison_entry(entry);

}

EXPORT_SYMBOL_GPL(is_hwpoison_address);