slab: Fix nodeid bounds check for non-contiguous node IDs

PATCH In review Paul Mackerras 5 participants 7 messages Dec 1, 2014 Memory management

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Paul Mackerras

author

2014-12-01 04:29 UTC #0 lore raw

PATCH v2 1/1 slab: Fix nodeid bounds check for non-contiguous node IDs

The bounds check for nodeid in ____cache_alloc_node gives false positives on machines where the node IDs are not contiguous, leading to a panic at boot time. For example, on a POWER8 machine the node IDs are typically 0, 1, 16 and 17. This means that num_online_nodes() returns 4, so when ____cache_alloc_node is called with nodeid = 16 the VM_BUG_ON triggers, like this:

kernel BUG at /home/paulus/kernel/kvm/mm/slab.c:3079!

Oops: Exception in kernel mode, sig: 5 [#1]
SMP NR_CPUS=1024 NUMA PowerNV
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 3.18.0-rc5-kvm+ #17
task: c0000000013ba230 ti: c000000001494000 task.ti: c000000001494000
NIP: c000000000264f6c LR: c000000000264f5c CTR: 0000000000000000
REGS: c0000000014979a0 TRAP: 0700   Not tainted  (3.18.0-rc5-kvm+)
MSR: 9000000002021032 <SF,HV,VEC,ME,IR,DR,RI>  CR: 28000448  XER: 20000000

CFAR: c00000000047e978 SOFTE: 0
GPR00: c000000000264f5c c000000001497c20 c000000001499d48 0000000000000004
GPR04: 0000000000000100 0000000000000010 0000000000000068 ffffffffffffffff
GPR08: 0000000000000000 0000000000000001 00000000082d0000 c000000000cca5a8
GPR12: 0000000048000448 c00000000fda0000 000001003bd44ff0 0000000010020578
GPR16: 000001003bd44ff8 000001003bd45000 0000000000000001 0000000000000000
GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000010
GPR24: c000000ffe000080 c000000000c824ec 0000000000000068 c000000ffe000080
GPR28: 0000000000000010 c000000ffe000080 0000000000000010 0000000000000000 NIP [c000000000264f6c] .____cache_alloc_node+0x6c/0x270
LR [c000000000264f5c] .____cache_alloc_node+0x5c/0x270

Call Trace:
[c000000001497c20] [c000000000264f5c] .____cache_alloc_node+0x5c/0x270 (unreliable)
[c000000001497cf0] [c00000000026552c] .kmem_cache_alloc_node_trace+0xdc/0x360
[c000000001497dc0] [c000000000c824ec] .init_list+0x3c/0x128
[c000000001497e50] [c000000000c827b4] .kmem_cache_init+0x1dc/0x258
[c000000001497ef0] [c000000000c54090] .start_kernel+0x2a0/0x568
[c000000001497f90] [c000000000008c6c] start_here_common+0x20/0xa8

Instruction dump:
7c7d1b78 7c962378 4bda4e91 60000000 3c620004 38800100 386370d8 48219959 60000000 7f83e000 7d301026 5529effe <0b090000> 393c0010 79291f24 7d3d4a14

To fix this, we instead compare the nodeid with MAX_NUMNODES, and additionally make sure it isn't negative (since nodeid is an int). The check is there mainly to protect the array dereference in the get_node() call in the next line, and the array being dereferenced is of size MAX_NUMNODES. If the nodeid is in range but invalid (for example if the node is off-line), the BUG_ON in the next line will catch that.

Signed-off-by Paul Mackerras <[email protected]>

---
v2: include the oops message in the patch description

 mm/slab.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

mm/slab.c +1 -1

index eb2b2ea..f34e053 100644
@@ -3076,7 +3076,7 @@ static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags,
 	void *obj;
 	int x;
 
-	VM_BUG_ON(nodeid > num_online_nodes());
+	VM_BUG_ON(nodeid < 0 || nodeid >= MAX_NUMNODES);
 	n = get_node(cachep, nodeid);
 	BUG_ON(!n);

Signature · 1 line

2.1.1

Yasuaki Ishimatsu

Reviewed-by on v2 1/1

2014-12-01 05:00 UTC #1 lore raw

Quoted 46 lines · Paul Mackerras

The bounds check for nodeid in ____cache_alloc_node gives false positives on machines where the node IDs are not contiguous, leading to a panic at boot time. For example, on a POWER8 machine the node IDs are typically 0, 1, 16 and 17. This means that num_online_nodes() returns 4, so when ____cache_alloc_node is called with nodeid = 16 the VM_BUG_ON triggers, like this:
kernel BUG at /home/paulus/kernel/kvm/mm/slab.c:3079!
Oops: Exception in kernel mode, sig: 5 [#1]
SMP NR_CPUS=1024 NUMA PowerNV
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 3.18.0-rc5-kvm+ #17
task: c0000000013ba230 ti: c000000001494000 task.ti: c000000001494000
NIP: c000000000264f6c LR: c000000000264f5c CTR: 0000000000000000
REGS: c0000000014979a0 TRAP: 0700   Not tainted  (3.18.0-rc5-kvm+)
MSR: 9000000002021032 <SF,HV,VEC,ME,IR,DR,RI>  CR: 28000448  XER: 20000000
CFAR: c00000000047e978 SOFTE: 0
GPR00: c000000000264f5c c000000001497c20 c000000001499d48 0000000000000004
GPR04: 0000000000000100 0000000000000010 0000000000000068 ffffffffffffffff
GPR08: 0000000000000000 0000000000000001 00000000082d0000 c000000000cca5a8
GPR12: 0000000048000448 c00000000fda0000 000001003bd44ff0 0000000010020578
GPR16: 000001003bd44ff8 000001003bd45000 0000000000000001 0000000000000000
GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000010
GPR24: c000000ffe000080 c000000000c824ec 0000000000000068 c000000ffe000080
GPR28: 0000000000000010 c000000ffe000080 0000000000000010 0000000000000000 NIP [c000000000264f6c] .____cache_alloc_node+0x6c/0x270
LR [c000000000264f5c] .____cache_alloc_node+0x5c/0x270
Call Trace:
[c000000001497c20] [c000000000264f5c] .____cache_alloc_node+0x5c/0x270 (unreliable)
[c000000001497cf0] [c00000000026552c] .kmem_cache_alloc_node_trace+0xdc/0x360
[c000000001497dc0] [c000000000c824ec] .init_list+0x3c/0x128
[c000000001497e50] [c000000000c827b4] .kmem_cache_init+0x1dc/0x258
[c000000001497ef0] [c000000000c54090] .start_kernel+0x2a0/0x568
[c000000001497f90] [c000000000008c6c] start_here_common+0x20/0xa8
Instruction dump:
7c7d1b78 7c962378 4bda4e91 60000000 3c620004 38800100 386370d8 48219959 60000000 7f83e000 7d301026 5529effe <0b090000> 393c0010 79291f24 7d3d4a14
To fix this, we instead compare the nodeid with MAX_NUMNODES, and additionally make sure it isn't negative (since nodeid is an int). The check is there mainly to protect the array dereference in the get_node() call in the next line, and the array being dereferenced is of size MAX_NUMNODES. If the nodeid is in range but invalid (for example if the node is off-line), the BUG_ON in the next line will catch that.

Quoted 2 lines

Signed-off-by Paul Mackerras <[email protected]>
---

Looks good to me.

Reviewed-by Yasuaki Ishimatsu <[email protected]>

If you need to backport it into -stable kernel, please read Documentation/stable_kernel_rules.txt.

Thanks,
Yasuaki Ishimatsu

Quoted 19 lines

v2: include the oops message in the patch description

  mm/slab.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

mm/slab.c +1 -1

index eb2b2ea..f34e053 100644
@@ -3076,7 +3076,7 @@ static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags,
  	void *obj;
  	int x;
 
-	VM_BUG_ON(nodeid > num_online_nodes());
+	VM_BUG_ON(nodeid < 0 || nodeid >= MAX_NUMNODES);
  	n = get_node(cachep, nodeid);
  	BUG_ON(!n);

Michael Ellerman

2014-12-01 05:02 UTC #2 lore raw

In reply to Paul Mackerras

Quoted 6 lines · Paul Mackerras

The bounds check for nodeid in ____cache_alloc_node gives false positives on machines where the node IDs are not contiguous, leading to a panic at boot time. For example, on a POWER8 machine the node IDs are typically 0, 1, 16 and 17. This means that num_online_nodes() returns 4, so when ____cache_alloc_node is called with nodeid = 16 the VM_BUG_ON triggers, like this:

...

Quoted 8 lines

To fix this, we instead compare the nodeid with MAX_NUMNODES, and additionally make sure it isn't negative (since nodeid is an int). The check is there mainly to protect the array dereference in the get_node() call in the next line, and the array being dereferenced is of size MAX_NUMNODES. If the nodeid is in range but invalid (for example if the node is off-line), the BUG_ON in the next line will catch that.

When did this break? How come we only just noticed?

Also needs:

Cc [email protected]

cheers

Paul Mackerras

author

2014-12-01 05:25 UTC #3 lore raw

Quoted 17 lines · Michael Ellerman

Quoted 6 lines · Paul Mackerras
The bounds check for nodeid in ____cache_alloc_node gives false positives on machines where the node IDs are not contiguous, leading to a panic at boot time. For example, on a POWER8 machine the node IDs are typically 0, 1, 16 and 17. This means that num_online_nodes() returns 4, so when ____cache_alloc_node is called with nodeid = 16 the VM_BUG_ON triggers, like this:
...
Quoted 8 lines
To fix this, we instead compare the nodeid with MAX_NUMNODES, and additionally make sure it isn't negative (since nodeid is an int). The check is there mainly to protect the array dereference in the get_node() call in the next line, and the array being dereferenced is of size MAX_NUMNODES. If the nodeid is in range but invalid (for example if the node is off-line), the BUG_ON in the next line will catch that.

Quoted 1 line

When did this break? How come we only just noticed?

Commit 14e50c6a9bc2, which went into 3.10-rc1.

You'll only notice if you have CONFIG_SLAB=y and CONFIG_DEBUG_VM=y and you're running on a machine with discontiguous node IDs.

Quoted 3 lines

Also needs:
Cc [email protected]

It does. I remembered that a minute after I sent the patch.

Paul.

Michael Ellerman

2014-12-01 08:52 UTC #4 lore raw

Quoted 18 lines · Paul Mackerras

Quoted 17 lines · Michael Ellerman
Quoted 6 lines · Paul Mackerras
The bounds check for nodeid in ____cache_alloc_node gives false positives on machines where the node IDs are not contiguous, leading to a panic at boot time. For example, on a POWER8 machine the node IDs are typically 0, 1, 16 and 17. This means that num_online_nodes() returns 4, so when ____cache_alloc_node is called with nodeid = 16 the VM_BUG_ON triggers, like this:
...
Quoted 8 lines
To fix this, we instead compare the nodeid with MAX_NUMNODES, and additionally make sure it isn't negative (since nodeid is an int). The check is there mainly to protect the array dereference in the get_node() call in the next line, and the array being dereferenced is of size MAX_NUMNODES. If the nodeid is in range but invalid (for example if the node is off-line), the BUG_ON in the next line will catch that.

Quoted 3 lines

Quoted 1 line
When did this break? How come we only just noticed?
Commit 14e50c6a9bc2, which went into 3.10-rc1.

OK. So a Fixes tag is nice:

Fixes 14e50c6a9bc2 ("mm: slab: Verify the nodeid passed to ____cache_alloc_node")

Quoted 2 lines

You'll only notice if you have CONFIG_SLAB=y and CONFIG_DEBUG_VM=y and you're running on a machine with discontiguous node IDs.

Right. And we have SLUB=y for all the defconfigs that are likely to hit that.

Quoted 5 lines

Quoted 3 lines
Also needs:
Cc [email protected]
It does. I remembered that a minute after I sent the patch.

OK. Hopefully one of the slab maintainers will be happy to add it for us when they merge this?

cheers

Pekka Enberg

Reviewed-by on v2 1/1

2014-12-01 09:22 UTC #5 lore raw

In reply to Paul Mackerras

Quoted 11 lines · Paul Mackerras

---
v2: include the oops message in the patch description
  mm/slab.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)
mm/slab.c +0 -0
index eb2b2ea..f34e053 100644

mm/slab.c static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags, · line 3081

Quoted 7 lines

mm/slab.c +1 -1

@@ -3076,7 +3076,7 @@ static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags,
  	void *obj;
  	int x;
 
-	VM_BUG_ON(nodeid > num_online_nodes());
+	VM_BUG_ON(nodeid < 0 || nodeid >= MAX_NUMNODES);
  	n = get_node(cachep, nodeid);
  	BUG_ON(!n);

Reviewed-by Pekka Enberg <[email protected]>

David Rientjes

Acked-by on v2 1/1

2014-12-01 21:06 UTC #6 lore raw

In reply to Paul Mackerras

Quoted 46 lines · Paul Mackerras

The bounds check for nodeid in ____cache_alloc_node gives false positives on machines where the node IDs are not contiguous, leading to a panic at boot time. For example, on a POWER8 machine the node IDs are typically 0, 1, 16 and 17. This means that num_online_nodes() returns 4, so when ____cache_alloc_node is called with nodeid = 16 the VM_BUG_ON triggers, like this:
kernel BUG at /home/paulus/kernel/kvm/mm/slab.c:3079!
Oops: Exception in kernel mode, sig: 5 [#1]
SMP NR_CPUS=1024 NUMA PowerNV
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 3.18.0-rc5-kvm+ #17
task: c0000000013ba230 ti: c000000001494000 task.ti: c000000001494000
NIP: c000000000264f6c LR: c000000000264f5c CTR: 0000000000000000
REGS: c0000000014979a0 TRAP: 0700   Not tainted  (3.18.0-rc5-kvm+)
MSR: 9000000002021032 <SF,HV,VEC,ME,IR,DR,RI>  CR: 28000448  XER: 20000000
CFAR: c00000000047e978 SOFTE: 0
GPR00: c000000000264f5c c000000001497c20 c000000001499d48 0000000000000004
GPR04: 0000000000000100 0000000000000010 0000000000000068 ffffffffffffffff
GPR08: 0000000000000000 0000000000000001 00000000082d0000 c000000000cca5a8
GPR12: 0000000048000448 c00000000fda0000 000001003bd44ff0 0000000010020578
GPR16: 000001003bd44ff8 000001003bd45000 0000000000000001 0000000000000000
GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000010
GPR24: c000000ffe000080 c000000000c824ec 0000000000000068 c000000ffe000080
GPR28: 0000000000000010 c000000ffe000080 0000000000000010 0000000000000000 NIP [c000000000264f6c] .____cache_alloc_node+0x6c/0x270
LR [c000000000264f5c] .____cache_alloc_node+0x5c/0x270
Call Trace:
[c000000001497c20] [c000000000264f5c] .____cache_alloc_node+0x5c/0x270 (unreliable)
[c000000001497cf0] [c00000000026552c] .kmem_cache_alloc_node_trace+0xdc/0x360
[c000000001497dc0] [c000000000c824ec] .init_list+0x3c/0x128
[c000000001497e50] [c000000000c827b4] .kmem_cache_init+0x1dc/0x258
[c000000001497ef0] [c000000000c54090] .start_kernel+0x2a0/0x568
[c000000001497f90] [c000000000008c6c] start_here_common+0x20/0xa8
Instruction dump:
7c7d1b78 7c962378 4bda4e91 60000000 3c620004 38800100 386370d8 48219959 60000000 7f83e000 7d301026 5529effe <0b090000> 393c0010 79291f24 7d3d4a14
To fix this, we instead compare the nodeid with MAX_NUMNODES, and additionally make sure it isn't negative (since nodeid is an int). The check is there mainly to protect the array dereference in the get_node() call in the next line, and the array being dereferenced is of size MAX_NUMNODES. If the nodeid is in range but invalid (for example if the node is off-line), the BUG_ON in the next line will catch that.

Quoted 1 line

Signed-off-by Paul Mackerras <[email protected]>

Acked-by David Rientjes <[email protected]>

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