linux-kernel - [PATCH 3.16 260/346] kvm-arm: Unmap shadow pagetables properly

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Message-ID: <lsq.1479082460.938900674@decadent.org.uk>
Date:   Mon, 14 Nov 2016 00:14:20 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "James Morse" <james.morse@....com>,
        "Christoffer Dall" <christoffer.dall@...aro.org>,
        "Marc Zyngier" <marc.zyngier@....com>,
        "Suzuki K Poulose" <suzuki.poulose@....com>,
        "Catalin Marinas" <catalin.marinas@....com>,
        "Itaru Kitayama" <itaru.kitayama@...en.jp>
Subject: [PATCH 3.16 260/346] kvm-arm: Unmap shadow pagetables properly

3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Suzuki K Poulose <suzuki.poulose@....com>

commit 293f293637b55db4f9f522a5a72514e98a541076 upstream.

On arm/arm64, we depend on the kvm_unmap_hva* callbacks (via
mmu_notifiers::invalidate_*) to unmap the stage2 pagetables when
the userspace buffer gets unmapped. However, when the Hypervisor
process exits without explicit unmap of the guest buffers, the only
notifier we get is kvm_arch_flush_shadow_all() (via mmu_notifier::release
) which does nothing on arm. Later this causes us to access pages that
were already released [via exit_mmap() -> unmap_vmas()] when we actually
get to unmap the stage2 pagetable [via kvm_arch_destroy_vm() ->
kvm_free_stage2_pgd()]. This triggers crashes with CONFIG_DEBUG_PAGEALLOC,
which unmaps any free'd pages from the linear map.

 [  757.644120] Unable to handle kernel paging request at virtual address
  ffff800661e00000
 [  757.652046] pgd = ffff20000b1a2000
 [  757.655471] [ffff800661e00000] *pgd=00000047fffe3003, *pud=00000047fcd8c003,
  *pmd=00000047fcc7c003, *pte=00e8004661e00712
 [  757.666492] Internal error: Oops: 96000147 [#3] PREEMPT SMP
 [  757.672041] Modules linked in:
 [  757.675100] CPU: 7 PID: 3630 Comm: qemu-system-aar Tainted: G      D
 4.8.0-rc1 #3
 [  757.683240] Hardware name: AppliedMicro X-Gene Mustang Board/X-Gene Mustang Board,
  BIOS 3.06.15 Aug 19 2016
 [  757.692938] task: ffff80069cdd3580 task.stack: ffff8006adb7c000
 [  757.698840] PC is at __flush_dcache_area+0x1c/0x40
 [  757.703613] LR is at kvm_flush_dcache_pmd+0x60/0x70
 [  757.708469] pc : [<ffff20000809dbdc>] lr : [<ffff2000080b4a70>] pstate: 20000145
 ...
 [  758.357249] [<ffff20000809dbdc>] __flush_dcache_area+0x1c/0x40
 [  758.363059] [<ffff2000080b6748>] unmap_stage2_range+0x458/0x5f0
 [  758.368954] [<ffff2000080b708c>] kvm_free_stage2_pgd+0x34/0x60
 [  758.374761] [<ffff2000080b2280>] kvm_arch_destroy_vm+0x20/0x68
 [  758.380570] [<ffff2000080aa330>] kvm_put_kvm+0x210/0x358
 [  758.385860] [<ffff2000080aa524>] kvm_vm_release+0x2c/0x40
 [  758.391239] [<ffff2000082ad234>] __fput+0x114/0x2e8
 [  758.396096] [<ffff2000082ad46c>] ____fput+0xc/0x18
 [  758.400869] [<ffff200008104658>] task_work_run+0x108/0x138
 [  758.406332] [<ffff2000080dc8ec>] do_exit+0x48c/0x10e8
 [  758.411363] [<ffff2000080dd5fc>] do_group_exit+0x6c/0x130
 [  758.416739] [<ffff2000080ed924>] get_signal+0x284/0xa18
 [  758.421943] [<ffff20000808a098>] do_signal+0x158/0x860
 [  758.427060] [<ffff20000808aad4>] do_notify_resume+0x6c/0x88
 [  758.432608] [<ffff200008083624>] work_pending+0x10/0x14
 [  758.437812] Code: 9ac32042 8b010001 d1000443 8a230000 (d50b7e20)

This patch fixes the issue by moving the kvm_free_stage2_pgd() to
kvm_arch_flush_shadow_all().

Tested-by: Itaru Kitayama <itaru.kitayama@...en.jp>
Reported-by: Itaru Kitayama <itaru.kitayama@...en.jp>
Reported-by: James Morse <james.morse@....com>
Cc: Marc Zyngier <marc.zyngier@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Christoffer Dall <christoffer.dall@...aro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
Signed-off-by: Christoffer Dall <christoffer.dall@...aro.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arm/kvm/arm.c | 2 --
 arch/arm/kvm/mmu.c | 1 +
 2 files changed, 1 insertion(+), 2 deletions(-)

--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -164,8 +164,6 @@ void kvm_arch_destroy_vm(struct kvm *kvm
 {
 	int i;
 
-	kvm_free_stage2_pgd(kvm);
-
 	for (i = 0; i < KVM_MAX_VCPUS; ++i) {
 		if (kvm->vcpus[i]) {
 			kvm_arch_vcpu_free(kvm->vcpus[i]);
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -1257,6 +1257,7 @@ void kvm_arch_memslots_updated(struct kv
 
 void kvm_arch_flush_shadow_all(struct kvm *kvm)
 {
+	kvm_free_stage2_pgd(kvm);
 }
 
 void kvm_arch_flush_shadow_memslot(struct kvm *kvm,