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.ga...@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 {