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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Lai Jiangshan <laijs@linux.alibaba.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Ovidiu Panait <ovidiu.panait@windriver.com>
Subject: [PATCH 4.14 22/23] KVM: X86: MMU: Use the correct inherited permissions to get shadow page
Date: Wed,  1 Sep 2021 14:27:07 +0200	[thread overview]
Message-ID: <20210901122250.495140430@linuxfoundation.org> (raw)
In-Reply-To: <20210901122249.786673285@linuxfoundation.org>

From: Lai Jiangshan <laijs@linux.alibaba.com>

commit b1bd5cba3306691c771d558e94baa73e8b0b96b7 upstream.

When computing the access permissions of a shadow page, use the effective
permissions of the walk up to that point, i.e. the logic AND of its parents'
permissions.  Two guest PxE entries that point at the same table gfn need to
be shadowed with different shadow pages if their parents' permissions are
different.  KVM currently uses the effective permissions of the last
non-leaf entry for all non-leaf entries.  Because all non-leaf SPTEs have
full ("uwx") permissions, and the effective permissions are recorded only
in role.access and merged into the leaves, this can lead to incorrect
reuse of a shadow page and eventually to a missing guest protection page
fault.

For example, here is a shared pagetable:

   pgd[]   pud[]        pmd[]            virtual address pointers
                     /->pmd1(u--)->pte1(uw-)->page1 <- ptr1 (u--)
        /->pud1(uw-)--->pmd2(uw-)->pte2(uw-)->page2 <- ptr2 (uw-)
   pgd-|           (shared pmd[] as above)
        \->pud2(u--)--->pmd1(u--)->pte1(uw-)->page1 <- ptr3 (u--)
                     \->pmd2(uw-)->pte2(uw-)->page2 <- ptr4 (u--)

  pud1 and pud2 point to the same pmd table, so:
  - ptr1 and ptr3 points to the same page.
  - ptr2 and ptr4 points to the same page.

(pud1 and pud2 here are pud entries, while pmd1 and pmd2 here are pmd entries)

- First, the guest reads from ptr1 first and KVM prepares a shadow
  page table with role.access=u--, from ptr1's pud1 and ptr1's pmd1.
  "u--" comes from the effective permissions of pgd, pud1 and
  pmd1, which are stored in pt->access.  "u--" is used also to get
  the pagetable for pud1, instead of "uw-".

- Then the guest writes to ptr2 and KVM reuses pud1 which is present.
  The hypervisor set up a shadow page for ptr2 with pt->access is "uw-"
  even though the pud1 pmd (because of the incorrect argument to
  kvm_mmu_get_page in the previous step) has role.access="u--".

- Then the guest reads from ptr3.  The hypervisor reuses pud1's
  shadow pmd for pud2, because both use "u--" for their permissions.
  Thus, the shadow pmd already includes entries for both pmd1 and pmd2.

- At last, the guest writes to ptr4.  This causes no vmexit or pagefault,
  because pud1's shadow page structures included an "uw-" page even though
  its role.access was "u--".

Any kind of shared pagetable might have the similar problem when in
virtual machine without TDP enabled if the permissions are different
from different ancestors.

In order to fix the problem, we change pt->access to be an array, and
any access in it will not include permissions ANDed from child ptes.

The test code is: https://lore.kernel.org/kvm/20210603050537.19605-1-jiangshanlai@gmail.com/
Remember to test it with TDP disabled.

The problem had existed long before the commit 41074d07c78b ("KVM: MMU:
Fix inherited permissions for emulated guest pte updates"), and it
is hard to find which is the culprit.  So there is no fixes tag here.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20210603052455.21023-1-jiangshanlai@gmail.com>
Cc: stable@vger.kernel.org
Fixes: cea0f0e7ea54 ("[PATCH] KVM: MMU: Shadow page table caching")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[OP: - apply arch/x86/kvm/mmu/* changes to arch/x86/kvm
     - apply documentation changes to Documentation/virtual/kvm/mmu.txt
     - add vcpu parameter to gpte_access() call]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 Documentation/virtual/kvm/mmu.txt |    4 ++--
 arch/x86/kvm/paging_tmpl.h        |   14 +++++++++-----
 2 files changed, 11 insertions(+), 7 deletions(-)

--- a/Documentation/virtual/kvm/mmu.txt
+++ b/Documentation/virtual/kvm/mmu.txt
@@ -152,8 +152,8 @@ Shadow pages contain the following infor
     shadow pages) so role.quadrant takes values in the range 0..3.  Each
     quadrant maps 1GB virtual address space.
   role.access:
-    Inherited guest access permissions in the form uwx.  Note execute
-    permission is positive, not negative.
+    Inherited guest access permissions from the parent ptes in the form uwx.
+    Note execute permission is positive, not negative.
   role.invalid:
     The page is invalid and should not be used.  It is a root page that is
     currently pinned (by a cpu hardware register pointing to it); once it is
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -93,8 +93,8 @@ struct guest_walker {
 	gpa_t pte_gpa[PT_MAX_FULL_LEVELS];
 	pt_element_t __user *ptep_user[PT_MAX_FULL_LEVELS];
 	bool pte_writable[PT_MAX_FULL_LEVELS];
-	unsigned pt_access;
-	unsigned pte_access;
+	unsigned int pt_access[PT_MAX_FULL_LEVELS];
+	unsigned int pte_access;
 	gfn_t gfn;
 	struct x86_exception fault;
 };
@@ -388,13 +388,15 @@ retry_walk:
 		}
 
 		walker->ptes[walker->level - 1] = pte;
+
+		/* Convert to ACC_*_MASK flags for struct guest_walker.  */
+		walker->pt_access[walker->level - 1] = FNAME(gpte_access)(vcpu, pt_access ^ walk_nx_mask);
 	} while (!is_last_gpte(mmu, walker->level, pte));
 
 	pte_pkey = FNAME(gpte_pkeys)(vcpu, pte);
 	accessed_dirty = have_ad ? pte_access & PT_GUEST_ACCESSED_MASK : 0;
 
 	/* Convert to ACC_*_MASK flags for struct guest_walker.  */
-	walker->pt_access = FNAME(gpte_access)(vcpu, pt_access ^ walk_nx_mask);
 	walker->pte_access = FNAME(gpte_access)(vcpu, pte_access ^ walk_nx_mask);
 	errcode = permission_fault(vcpu, mmu, walker->pte_access, pte_pkey, access);
 	if (unlikely(errcode))
@@ -433,7 +435,8 @@ retry_walk:
 	}
 
 	pgprintk("%s: pte %llx pte_access %x pt_access %x\n",
-		 __func__, (u64)pte, walker->pte_access, walker->pt_access);
+		 __func__, (u64)pte, walker->pte_access,
+		 walker->pt_access[walker->level - 1]);
 	return 1;
 
 error:
@@ -602,7 +605,7 @@ static int FNAME(fetch)(struct kvm_vcpu
 {
 	struct kvm_mmu_page *sp = NULL;
 	struct kvm_shadow_walk_iterator it;
-	unsigned direct_access, access = gw->pt_access;
+	unsigned int direct_access, access;
 	int top_level, ret;
 	gfn_t gfn, base_gfn;
 
@@ -634,6 +637,7 @@ static int FNAME(fetch)(struct kvm_vcpu
 		sp = NULL;
 		if (!is_shadow_present_pte(*it.sptep)) {
 			table_gfn = gw->table_gfn[it.level - 2];
+			access = gw->pt_access[it.level - 2];
 			sp = kvm_mmu_get_page(vcpu, table_gfn, addr, it.level-1,
 					      false, access);
 		}



  parent reply	other threads:[~2021-09-01 12:29 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-01 12:26 [PATCH 4.14 00/23] 4.14.246-rc1 review Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 01/23] ARC: Fix CONFIG_STACKDEPOT Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 02/23] can: usb: esd_usb2: esd_usb2_rx_event(): fix the interchange of the CAN RX and TX error counters Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 03/23] Revert "USB: serial: ch341: fix character loss at high transfer rates" Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 04/23] USB: serial: option: add new VID/PID to support Fibocom FG150 Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 05/23] usb: dwc3: gadget: Fix dwc3_calc_trbs_left() Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 06/23] usb: dwc3: gadget: Stop EP0 transfers during pullup disable Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 07/23] IB/hfi1: Fix possible null-pointer dereference in _extend_sdma_tx_descs() Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 08/23] e1000e: Fix the max snoop/no-snoop latency for 10M Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 09/23] ip_gre: add validation for csum_start Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 10/23] xgene-v2: Fix a resource leak in the error handling path of xge_probe() Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 11/23] net: marvell: fix MVNETA_TX_IN_PRGRS bit number Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 12/23] usb: gadget: u_audio: fix race condition on endpoint stop Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 13/23] opp: remove WARN when no valid OPPs remain Greg Kroah-Hartman
2021-09-01 12:26 ` [PATCH 4.14 14/23] virtio: Improve vq->broken access to avoid any compiler optimization Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 15/23] vringh: Use wiov->used to check for read/write desc order Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 16/23] drm: Copy drm_wait_vblank to user before returning Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 17/23] drm/nouveau/disp: power down unused DP links during init Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 18/23] net/rds: dma_map_sg is entitled to merge entries Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 19/23] vt_kdsetmode: extend console locking Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 20/23] fbmem: add margin check to fb_check_caps() Greg Kroah-Hartman
2021-09-01 12:27 ` [PATCH 4.14 21/23] KVM: x86/mmu: Treat NX as used (not reserved) for all !TDP shadow MMUs Greg Kroah-Hartman
2021-09-01 12:27 ` Greg Kroah-Hartman [this message]
2021-09-01 12:27 ` [PATCH 4.14 23/23] Revert "floppy: reintroduce O_NDELAY fix" Greg Kroah-Hartman
2021-09-01 19:21 ` [PATCH 4.14 00/23] 4.14.246-rc1 review Jon Hunter
2021-09-01 19:22 ` Jon Hunter
2021-09-02  1:08 ` Samuel Zou
2021-09-02 16:08 ` Naresh Kamboju
2021-09-02 21:50 ` Guenter Roeck

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