From 6503bd6a1b5364ffd346a8a475e1eb91b9f756e5 Mon Sep 17 00:00:00 2001 From: Ross Lagerwall Date: Mon, 24 Jan 2022 10:44:50 +0000 Subject: [PATCH] xen-mapcache: Avoid entry->lock overflow In some cases, a particular mapcache entry may be mapped 256 times causing the lock field to wrap to 0. For example, this may happen when using emulated NVME and the guest submits a large scatter-gather write. At this point, the entry map be remapped causing QEMU to write the wrong data or crash (since remap is not atomic). Avoid this overflow by increasing the lock field to a uint32_t and also detect it and abort rather than continuing regardless. Signed-off-by: Ross Lagerwall Reviewed-by: Paul Durrant Reviewed-by: Stefano Stabellini Message-Id: <20220124104450.152481-1-ross.lagerwall@citrix.com> Signed-off-by: Anthony PERARD (cherry picked from commit a021a2dd8b790437d27db95774969349632f856a) --- hw/i386/xen/xen-mapcache.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/hw/i386/xen/xen-mapcache.c b/hw/i386/xen/xen-mapcache.c index 5b120ed44b..c66f582da1 100644 --- a/hw/i386/xen/xen-mapcache.c +++ b/hw/i386/xen/xen-mapcache.c @@ -52,7 +52,7 @@ typedef struct MapCacheEntry { hwaddr paddr_index; uint8_t *vaddr_base; unsigned long *valid_mapping; - uint8_t lock; + uint32_t lock; #define XEN_MAPCACHE_ENTRY_DUMMY (1 << 0) uint8_t flags; hwaddr size; @@ -341,6 +341,12 @@ tryagain: if (lock) { MapCacheRev *reventry = g_malloc0(sizeof(MapCacheRev)); entry->lock++; + if (entry->lock == 0) { + fprintf(stderr, + "mapcache entry lock overflow: "TARGET_FMT_plx" -> %p\n", + entry->paddr_index, entry->vaddr_base); + abort(); + } reventry->dma = dma; reventry->vaddr_req = mapcache->last_entry->vaddr_base + address_offset; reventry->paddr_index = mapcache->last_entry->paddr_index; -- 2.39.5