On 12/06/17 08:59, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
>
> The patch below does not apply to the 4.11-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.
>
> thanks,
>
> greg k-h
>
> ------------------ original commit in Linus's tree ------------------
>
> From d6dbdd3c8558cad3b6d74cc357b408622d122331 Mon Sep 17 00:00:00 2001
> From: Marc Zyngier <marc.zyngier@xxxxxxx>
> Date: Mon, 5 Jun 2017 19:17:18 +0100
> Subject: [PATCH] KVM: arm/arm64: Handle possible NULL stage2 pud when ageing
> pages
>
> Under memory pressure, we start ageing pages, which amounts to parsing
> the page tables. Since we don't want to allocate any extra level,
> we pass NULL for our private allocation cache. Which means that
> stage2_get_pud() is allowed to fail. This results in the following
> splat:
>
> [ 1520.409577] Unable to handle kernel NULL pointer dereference at virtual address 00000008
> [ 1520.417741] pgd = ffff810f52fef000
> [ 1520.421201] [00000008] *pgd=0000010f636c5003, *pud=0000010f56f48003, *pmd=0000000000000000
> [ 1520.429546] Internal error: Oops: 96000006 [#1] PREEMPT SMP
> [ 1520.435156] Modules linked in:
> [ 1520.438246] CPU: 15 PID: 53550 Comm: qemu-system-aar Tainted: G W 4.12.0-rc4-00027-g1885c397eaec #7205
> [ 1520.448705] Hardware name: FOXCONN R2-1221R-A4/C2U4N_MB, BIOS G31FB12A 10/26/2016
> [ 1520.463726] task: ffff800ac5fb4e00 task.stack: ffff800ce04e0000
> [ 1520.469666] PC is at stage2_get_pmd+0x34/0x110
> [ 1520.474119] LR is at kvm_age_hva_handler+0x44/0xf0
> [ 1520.478917] pc : [<ffff0000080b137c>] lr : [<ffff0000080b149c>] pstate: 40000145
> [ 1520.486325] sp : ffff800ce04e33d0
> [ 1520.489644] x29: ffff800ce04e33d0 x28: 0000000ffff40064
> [ 1520.494967] x27: 0000ffff27e00000 x26: 0000000000000000
> [ 1520.500289] x25: ffff81051ba65008 x24: 0000ffff40065000
> [ 1520.505618] x23: 0000ffff40064000 x22: 0000000000000000
> [ 1520.510947] x21: ffff810f52b20000 x20: 0000000000000000
> [ 1520.516274] x19: 0000000058264000 x18: 0000000000000000
> [ 1520.521603] x17: 0000ffffa6fe7438 x16: ffff000008278b70
> [ 1520.526940] x15: 000028ccd8000000 x14: 0000000000000008
> [ 1520.532264] x13: ffff7e0018298000 x12: 0000000000000002
> [ 1520.537582] x11: ffff000009241b93 x10: 0000000000000940
> [ 1520.542908] x9 : ffff0000092ef800 x8 : 0000000000000200
> [ 1520.548229] x7 : ffff800ce04e36a8 x6 : 0000000000000000
> [ 1520.553552] x5 : 0000000000000001 x4 : 0000000000000000
> [ 1520.558873] x3 : 0000000000000000 x2 : 0000000000000008
> [ 1520.571696] x1 : ffff000008fd5000 x0 : ffff0000080b149c
> [ 1520.577039] Process qemu-system-aar (pid: 53550, stack limit = 0xffff800ce04e0000)
> [...]
> [ 1521.510735] [<ffff0000080b137c>] stage2_get_pmd+0x34/0x110
> [ 1521.516221] [<ffff0000080b149c>] kvm_age_hva_handler+0x44/0xf0
> [ 1521.522054] [<ffff0000080b0610>] handle_hva_to_gpa+0xb8/0xe8
> [ 1521.527716] [<ffff0000080b3434>] kvm_age_hva+0x44/0xf0
> [ 1521.532854] [<ffff0000080a58b0>] kvm_mmu_notifier_clear_flush_young+0x70/0xc0
> [ 1521.539992] [<ffff000008238378>] __mmu_notifier_clear_flush_young+0x88/0xd0
> [ 1521.546958] [<ffff00000821eca0>] page_referenced_one+0xf0/0x188
> [ 1521.552881] [<ffff00000821f36c>] rmap_walk_anon+0xec/0x250
> [ 1521.558370] [<ffff000008220f78>] rmap_walk+0x78/0xa0
> [ 1521.563337] [<ffff000008221104>] page_referenced+0x164/0x180
> [ 1521.569002] [<ffff0000081f1af0>] shrink_active_list+0x178/0x3b8
> [ 1521.574922] [<ffff0000081f2058>] shrink_node_memcg+0x328/0x600
> [ 1521.580758] [<ffff0000081f23f4>] shrink_node+0xc4/0x328
> [ 1521.585986] [<ffff0000081f2718>] do_try_to_free_pages+0xc0/0x340
> [ 1521.592000] [<ffff0000081f2a64>] try_to_free_pages+0xcc/0x240
> [...]
>
> The trivial fix is to handle this NULL pud value early, rather than
> dereferencing it blindly.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> Reviewed-by: Christoffer Dall <cdall@xxxxxxxxxx>
> Signed-off-by: Christoffer Dall <cdall@xxxxxxxxxx>
Here's the patch that applies to both 4.9 and 4.11. I'll send a 4.4
backport shortly.
>From 35d3c4e744745ff32415aedcad72a105bfb9a1f7 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <marc.zyngier@xxxxxxx>
Date: Mon, 5 Jun 2017 19:17:18 +0100
Subject: [PATCH] KVM: arm/arm64: Handle possible NULL stage2 pud when ageing
pages
Commit d6dbdd3c8558cad3b6d74cc357b408622d122331 upstream.
Under memory pressure, we start ageing pages, which amounts to parsing
the page tables. Since we don't want to allocate any extra level,
we pass NULL for our private allocation cache. Which means that
stage2_get_pud() is allowed to fail. This results in the following
splat:
[ 1520.409577] Unable to handle kernel NULL pointer dereference at virtual address 00000008
[ 1520.417741] pgd = ffff810f52fef000
[ 1520.421201] [00000008] *pgd=0000010f636c5003, *pud=0000010f56f48003, *pmd=0000000000000000
[ 1520.429546] Internal error: Oops: 96000006 [#1] PREEMPT SMP
[ 1520.435156] Modules linked in:
[ 1520.438246] CPU: 15 PID: 53550 Comm: qemu-system-aar Tainted: G W 4.12.0-rc4-00027-g1885c397eaec #7205
[ 1520.448705] Hardware name: FOXCONN R2-1221R-A4/C2U4N_MB, BIOS G31FB12A 10/26/2016
[ 1520.463726] task: ffff800ac5fb4e00 task.stack: ffff800ce04e0000
[ 1520.469666] PC is at stage2_get_pmd+0x34/0x110
[ 1520.474119] LR is at kvm_age_hva_handler+0x44/0xf0
[ 1520.478917] pc : [<ffff0000080b137c>] lr : [<ffff0000080b149c>] pstate: 40000145
[ 1520.486325] sp : ffff800ce04e33d0
[ 1520.489644] x29: ffff800ce04e33d0 x28: 0000000ffff40064
[ 1520.494967] x27: 0000ffff27e00000 x26: 0000000000000000
[ 1520.500289] x25: ffff81051ba65008 x24: 0000ffff40065000
[ 1520.505618] x23: 0000ffff40064000 x22: 0000000000000000
[ 1520.510947] x21: ffff810f52b20000 x20: 0000000000000000
[ 1520.516274] x19: 0000000058264000 x18: 0000000000000000
[ 1520.521603] x17: 0000ffffa6fe7438 x16: ffff000008278b70
[ 1520.526940] x15: 000028ccd8000000 x14: 0000000000000008
[ 1520.532264] x13: ffff7e0018298000 x12: 0000000000000002
[ 1520.537582] x11: ffff000009241b93 x10: 0000000000000940
[ 1520.542908] x9 : ffff0000092ef800 x8 : 0000000000000200
[ 1520.548229] x7 : ffff800ce04e36a8 x6 : 0000000000000000
[ 1520.553552] x5 : 0000000000000001 x4 : 0000000000000000
[ 1520.558873] x3 : 0000000000000000 x2 : 0000000000000008
[ 1520.571696] x1 : ffff000008fd5000 x0 : ffff0000080b149c
[ 1520.577039] Process qemu-system-aar (pid: 53550, stack limit = 0xffff800ce04e0000)
[...]
[ 1521.510735] [<ffff0000080b137c>] stage2_get_pmd+0x34/0x110
[ 1521.516221] [<ffff0000080b149c>] kvm_age_hva_handler+0x44/0xf0
[ 1521.522054] [<ffff0000080b0610>] handle_hva_to_gpa+0xb8/0xe8
[ 1521.527716] [<ffff0000080b3434>] kvm_age_hva+0x44/0xf0
[ 1521.532854] [<ffff0000080a58b0>] kvm_mmu_notifier_clear_flush_young+0x70/0xc0
[ 1521.539992] [<ffff000008238378>] __mmu_notifier_clear_flush_young+0x88/0xd0
[ 1521.546958] [<ffff00000821eca0>] page_referenced_one+0xf0/0x188
[ 1521.552881] [<ffff00000821f36c>] rmap_walk_anon+0xec/0x250
[ 1521.558370] [<ffff000008220f78>] rmap_walk+0x78/0xa0
[ 1521.563337] [<ffff000008221104>] page_referenced+0x164/0x180
[ 1521.569002] [<ffff0000081f1af0>] shrink_active_list+0x178/0x3b8
[ 1521.574922] [<ffff0000081f2058>] shrink_node_memcg+0x328/0x600
[ 1521.580758] [<ffff0000081f23f4>] shrink_node+0xc4/0x328
[ 1521.585986] [<ffff0000081f2718>] do_try_to_free_pages+0xc0/0x340
[ 1521.592000] [<ffff0000081f2a64>] try_to_free_pages+0xcc/0x240
[...]
The trivial fix is to handle this NULL pud value early, rather than
dereferencing it blindly.
Cc: stable@xxxxxxxxxxxxxxx #4.9, 4.11
Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Reviewed-by: Christoffer Dall <cdall@xxxxxxxxxx>
Signed-off-by: Christoffer Dall <cdall@xxxxxxxxxx>
---
arch/arm/kvm/mmu.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 3837b096e1a6..b97bc12812ab 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -879,6 +879,9 @@ static pmd_t *stage2_get_pmd(struct kvm *kvm, struct kvm_mmu_memory_cache *cache
pmd_t *pmd;
pud = stage2_get_pud(kvm, cache, addr);
+ if (!pud)
+ return NULL;
+
if (stage2_pud_none(*pud)) {
if (!cache)
return NULL;
--
2.11.0
--
Jazz is not dead. It just smells funny...