Re: [RESEND PATCH v3 2/4] iommu/iova: Avoid double-negatives in magazine helpers
From: John Garry
Date: Wed Dec 09 2020 - 06:41:01 EST
On 09/12/2020 09:03, Leizhen (ThunderTown) wrote:
On 2020/11/17 18:25, John Garry wrote:
A similar crash to the following could be observed if initial CPU rcache
magazine allocations fail in init_iova_rcaches():
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Mem abort info:
ESR = 0x96000004
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
Data abort info:
ISV = 0, ISS = 0x00000004
CM = 0, WnR = 0
[0000000000000000] user address but active_mm is swapper
Internal error: Oops: 96000004 [#1] PREEMPT SMP
Modules linked in:
CPU: 11 PID: 696 Comm: irq/40-hisi_sas Not tainted 5.9.0-rc7-dirty #109
Hardware name: Huawei D06 /D06, BIOS Hisilicon D06 UEFI RC0 - V1.16.01 03/15/2019
Call trace:
free_iova_fast+0xfc/0x280
iommu_dma_free_iova+0x64/0x70
__iommu_dma_unmap+0x9c/0xf8
iommu_dma_unmap_sg+0xa8/0xc8
dma_unmap_sg_attrs+0x28/0x50
cq_thread_v3_hw+0x2dc/0x528
irq_thread_fn+0x2c/0xa0
irq_thread+0x130/0x1e0
kthread+0x154/0x158
ret_from_fork+0x10/0x34
Code: f9400060 f102001f 54000981 d4210000 (f9400043)
---[ end trace 4afcbdfc61b60467 ]---
The issue is that expression !iova_magazine_full(NULL) evaluates true; this
falls over in in __iova_rcache_insert() when we attempt to cache a mag
and cpu_rcache->loaded == NULL:
if (!iova_magazine_full(cpu_rcache->loaded)) {
can_insert = true;
...
if (can_insert)
iova_magazine_push(cpu_rcache->loaded, iova_pfn);
As above, can_insert is evaluated true, which it shouldn't be, and we try
to insert pfns in a NULL mag, which is not safe.
To avoid this, stop using double-negatives, like !iova_magazine_full() and
!iova_magazine_empty(), and use positive tests, like
iova_magazine_has_space() and iova_magazine_has_pfns(), respectively; these
can safely deal with cpu_rcache->{loaded, prev} = NULL.
Signed-off-by: John Garry <john.garry@xxxxxxxxxx>
Thanks for checking here...
---
drivers/iommu/iova.c | 29 +++++++++++++++++------------
1 file changed, 17 insertions(+), 12 deletions(-)
diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index 81b7399dd5e8..1f3f0f8b12e0 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -827,14 +827,18 @@ iova_magazine_free_pfns(struct iova_magazine *mag, struct iova_domain *iovad)
mag->size = 0;
}
-static bool iova_magazine_full(struct iova_magazine *mag)
+static bool iova_magazine_has_space(struct iova_magazine *mag)
{
- return (mag && mag->size == IOVA_MAG_SIZE);
+ if (!mag)
+ return false;
+ return mag->size < IOVA_MAG_SIZE;
}
-static bool iova_magazine_empty(struct iova_magazine *mag)
+static bool iova_magazine_has_pfns(struct iova_magazine *mag)
{
- return (!mag || mag->size == 0);
+ if (!mag)
+ return false;
+ return mag->size;
}
static unsigned long iova_magazine_pop(struct iova_magazine *mag,
@@ -843,7 +847,7 @@ static unsigned long iova_magazine_pop(struct iova_magazine *mag,
int i;
unsigned long pfn;
- BUG_ON(iova_magazine_empty(mag));
+ BUG_ON(!iova_magazine_has_pfns(mag));
/* Only fall back to the rbtree if we have no suitable pfns at all */
for (i = mag->size - 1; mag->pfns[i] > limit_pfn; i--)
@@ -859,7 +863,7 @@ static unsigned long iova_magazine_pop(struct iova_magazine *mag,
static void iova_magazine_push(struct iova_magazine *mag, unsigned long pfn)
{
- BUG_ON(iova_magazine_full(mag));
+ BUG_ON(!iova_magazine_has_space(mag));
mag->pfns[mag->size++] = pfn;
}
@@ -905,9 +909,9 @@ static bool __iova_rcache_insert(struct iova_domain *iovad,
cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches);
spin_lock_irqsave(&cpu_rcache->lock, flags);
- if (!iova_magazine_full(cpu_rcache->loaded)) {
*
+ if (iova_magazine_has_space(cpu_rcache->loaded)) {
can_insert = true;
- } else if (!iova_magazine_full(cpu_rcache->prev)) {
+ } else if (iova_magazine_has_space(cpu_rcache->prev)) {
swap(cpu_rcache->prev, cpu_rcache->loaded);
can_insert = true;
} else {
@@ -916,8 +920,9 @@ static bool __iova_rcache_insert(struct iova_domain *iovad,
if (new_mag) {
spin_lock(&rcache->lock);
if (rcache->depot_size < MAX_GLOBAL_MAGS) {
- rcache->depot[rcache->depot_size++] =
- cpu_rcache->loaded;
+ if (cpu_rcache->loaded)
Looks like it just needs to change this place. Compiler ensures that mag->size
will not be accessed when mag is NULL.
Not sure about that. We would get a crash prior to touching this codepath:
So if cpu_rcache->loaded == NULL at entry, then
!iova_magazine_full(cpu_rcache->loaded (==NULL) ) evaluates true, *
above, so can_insert is set true, and we then attempt
iova_magazine_push(cpu_rcache->loaded (==NULL), iova_pfn), which is not
safe.
ok?
Cheers,
John
static bool iova_magazine_full(struct iova_magazine *mag)
{
return (mag && mag->size == IOVA_MAG_SIZE);
}
static bool iova_magazine_empty(struct iova_magazine *mag)
{
return (!mag || mag->size == 0);
}
+ rcache->depot[rcache->depot_size++] =
+ cpu_rcache->loaded;
} else {
mag_to_free = cpu_rcache->loaded;
}
@@ -968,9 +973,9 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache,
cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches);
spin_lock_irqsave(&cpu_rcache->lock, flags);
- if (!iova_magazine_empty(cpu_rcache->loaded)) {
+ if (iova_magazine_has_pfns(cpu_rcache->loaded)) {
has_pfn = true;
- } else if (!iova_magazine_empty(cpu_rcache->prev)) {
+ } else if (iova_magazine_has_pfns(cpu_rcache->prev)) {
swap(cpu_rcache->prev, cpu_rcache->loaded);
has_pfn = true;
} else {