[PATCH 1/2] hw/ide: reset: cancel async DMA operation before reseting state

[Fiona Ebner <f.ebner@proxmox.com>]

If there is a pending DMA operation during ide_bus_reset(), the fact
that the IDEState is already reset before the operation is canceled
can be problematic. In particular, ide_dma_cb() might be called and
then use the reset IDEState which contains the signature after the
reset. When used to construct the IO operation this leads to
ide_get_sector() returning 0 and nsector being 1. This is particularly
bad, because a write command will thus destroy the first sector which
often contains a partition table or similar.

Traces showing the unsolicited write happening with IDEState
0x5595af6949d0 being used after reset:

> ahci_port_write ahci(0x5595af6923f0)[0]: port write [reg:PxSCTL] @ 0x2c: 0x00000300
> ahci_reset_port ahci(0x5595af6923f0)[0]: reset port
> ide_reset IDEstate 0x5595af6949d0
> ide_reset IDEstate 0x5595af694da8
> ide_bus_reset_aio aio_cancel
> dma_aio_cancel dbs=0x7f64600089a0
> dma_blk_cb dbs=0x7f64600089a0 ret=0
> dma_complete dbs=0x7f64600089a0 ret=0 cb=0x5595acd40b30
> ahci_populate_sglist ahci(0x5595af6923f0)[0]
> ahci_dma_prepare_buf ahci(0x5595af6923f0)[0]: prepare buf limit=512 prepared=512
> ide_dma_cb IDEState 0x5595af6949d0; sector_num=0 n=1 cmd=DMA WRITE
> dma_blk_io dbs=0x7f6420802010 bs=0x5595ae2c6c30 offset=0 to_dev=1
> dma_blk_cb dbs=0x7f6420802010 ret=0

> (gdb) p *qiov
> $11 = {iov = 0x7f647c76d840, niov = 1, {{nalloc = 1, local_iov = {iov_base = 0x0,
>       iov_len = 512}}, {__pad = "\001\000\000\000\000\000\000\000\000\000\000",
>       size = 512}}}
> (gdb) bt
> #0  blk_aio_pwritev (blk=0x5595ae2c6c30, offset=0, qiov=0x7f6420802070, flags=0,
>     cb=0x5595ace6f0b0 <dma_blk_cb>, opaque=0x7f6420802010)
>     at ../block/block-backend.c:1682
> #1  0x00005595ace6f185 in dma_blk_cb (opaque=0x7f6420802010, ret=<optimized out>)
>     at ../softmmu/dma-helpers.c:179
> #2  0x00005595ace6f778 in dma_blk_io (ctx=0x5595ae0609f0,
>     sg=sg@entry=0x5595af694d00, offset=offset@entry=0, align=align@entry=512,
>     io_func=io_func@entry=0x5595ace6ee30 <dma_blk_write_io_func>,
>     io_func_opaque=io_func_opaque@entry=0x5595ae2c6c30,
>     cb=0x5595acd40b30 <ide_dma_cb>, opaque=0x5595af6949d0,
>     dir=DMA_DIRECTION_TO_DEVICE) at ../softmmu/dma-helpers.c:244
> #3  0x00005595ace6f90a in dma_blk_write (blk=0x5595ae2c6c30,
>     sg=sg@entry=0x5595af694d00, offset=offset@entry=0, align=align@entry=512,
>     cb=cb@entry=0x5595acd40b30 <ide_dma_cb>, opaque=opaque@entry=0x5595af6949d0)
>     at ../softmmu/dma-helpers.c:280
> #4  0x00005595acd40e18 in ide_dma_cb (opaque=0x5595af6949d0, ret=<optimized out>)
>     at ../hw/ide/core.c:953
> #5  0x00005595ace6f319 in dma_complete (ret=0, dbs=0x7f64600089a0)
>     at ../softmmu/dma-helpers.c:107
> #6  dma_blk_cb (opaque=0x7f64600089a0, ret=0) at ../softmmu/dma-helpers.c:127
> #7  0x00005595ad12227d in blk_aio_complete (acb=0x7f6460005b10)
>     at ../block/block-backend.c:1527
> #8  blk_aio_complete (acb=0x7f6460005b10) at ../block/block-backend.c:1524
> #9  blk_aio_write_entry (opaque=0x7f6460005b10) at ../block/block-backend.c:1594
> #10 0x00005595ad258cfb in coroutine_trampoline (i0=<optimized out>,
>     i1=<optimized out>) at ../util/coroutine-ucontext.c:177

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 hw/ide/core.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/hw/ide/core.c b/hw/ide/core.c
index de48ff9f86..7e601a379a 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -2515,19 +2515,19 @@ static void ide_dummy_transfer_stop(IDEState *s)
 
 void ide_bus_reset(IDEBus *bus)
 {
-    bus->unit = 0;
-    bus->cmd = 0;
-    ide_reset(&bus->ifs[0]);
-    ide_reset(&bus->ifs[1]);
-    ide_clear_hob(bus);
-
-    /* pending async DMA */
+    /* pending async DMA - needs the IDEState before it is reset */
     if (bus->dma->aiocb) {
         trace_ide_bus_reset_aio();
         blk_aio_cancel(bus->dma->aiocb);
         bus->dma->aiocb = NULL;
     }
 
+    bus->unit = 0;
+    bus->cmd = 0;
+    ide_reset(&bus->ifs[0]);
+    ide_reset(&bus->ifs[1]);
+    ide_clear_hob(bus);
+
     /* reset dma provider too */
     if (bus->dma->ops->reset) {
         bus->dma->ops->reset(bus->dma);
-- 
2.39.2