linux-kernel - [PATCH] kvm/x86/mmu: use the correct inherited permissions to get shadow page

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Message-Id: <20201120095517.19211-1-jiangshanlai@gmail.com>
Date:   Fri, 20 Nov 2020 17:55:17 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Avi Kivity <avi@...ranet.com>, linux-doc@...r.kernel.org
Subject: [PATCH] kvm/x86/mmu: use the correct inherited permissions to get shadow page

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

Commit 41074d07c78b ("KVM: MMU: Fix inherited permissions for emulated
guest pte updates") said role.access is common access permissions for
all ptes in this shadow page, which is the inherited permissions from
the parent ptes.

But the commit did not enforce this definition when kvm_mmu_get_page()
is called in FNAME(fetch). Rather, it uses a random (last level pte's
combined) access permissions. And the permissions won't be checked again
in next FNAME(fetch) since the spte is present. It might fail to meet
guest's expectation when guest sets up spaghetti pagetables.

Fixes: 41074d07c78b ("KVM: MMU: Fix inherited permissions for emulated guest pte updates")
Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 Documentation/virt/kvm/mmu.rst |  4 ++--
 arch/x86/kvm/mmu/paging_tmpl.h | 14 +++++++++-----
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/Documentation/virt/kvm/mmu.rst b/Documentation/virt/kvm/mmu.rst
index 1c030dbac7c4..b31586504a9a 100644
--- a/Documentation/virt/kvm/mmu.rst
+++ b/Documentation/virt/kvm/mmu.rst
@@ -171,8 +171,8 @@ Shadow pages contain the following information:
     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
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 50e268eb8e1a..00a0bfaed6e8 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -90,8 +90,8 @@ 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;
 };
@@ -418,13 +418,15 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
 		}
 
 		walker->ptes[walker->level - 1] = pte;
+
+		/* Convert to ACC_*_MASK flags for struct guest_walker.  */
+		walker->pt_access[walker->level - 1] = FNAME(gpte_access)(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)(pt_access ^ walk_nx_mask);
 	walker->pte_access = FNAME(gpte_access)(pte_access ^ walk_nx_mask);
 	errcode = permission_fault(vcpu, mmu, walker->pte_access, pte_pkey, access);
 	if (unlikely(errcode))
@@ -463,7 +465,8 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
 	}
 
 	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:
@@ -635,7 +638,7 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, gpa_t addr,
 	bool huge_page_disallowed = exec && nx_huge_page_workaround_enabled;
 	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, level, req_level, ret;
 	gfn_t base_gfn = gw->gfn;
 
@@ -667,6 +670,7 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, gpa_t addr,
 		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);
 		}
-- 
2.19.1.6.gb485710b