Messages in this thread | | | Subject | Re: [RESEND PATCH v3 2/4] iommu/iova: Avoid double-negatives in magazine helpers | From | John Garry <> | Date | Wed, 9 Dec 2020 11:39:39 +0000 |
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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@huawei.com>
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 { >> >
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