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Re: [Qemu-devel] [PATCH v2] ide: ahci: add check before calling dma_memo
From: |
John Snow |
Subject: |
Re: [Qemu-devel] [PATCH v2] ide: ahci: add check before calling dma_memory_unmap |
Date: |
Thu, 28 Jan 2016 14:57:28 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 01/28/2016 02:48 PM, P J P wrote:
> From: Prasad J Pandit <address@hidden>
>
> When IDE AHCI emulation uses Frame Information Structures(FIS)
> engine for data transfer, the mapped FIS buffer address is stored
> in a static 'bounce.buffer'. When a request is made to map another
> memory region, address_space_map() returns NULL because
> 'bounce.buffer' is in_use. It leads to a null pointer dereference
> error while doing 'dma_memory_unmap'. Add a check to avoid it.
>
> Reported-by: Zuozhi fzz <address@hidden>
> Signed-off-by: Prasad J Pandit <address@hidden>
> ---
> hw/ide/ahci.c | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> Update as per review
> -> https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg05715.html
>
> diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
> index 17f1cbd..f413a59 100644
> --- a/hw/ide/ahci.c
> +++ b/hw/ide/ahci.c
> @@ -661,9 +661,11 @@ static bool ahci_map_fis_address(AHCIDevice *ad)
>
> static void ahci_unmap_fis_address(AHCIDevice *ad)
> {
> - dma_memory_unmap(ad->hba->as, ad->res_fis, 256,
> - DMA_DIRECTION_FROM_DEVICE, 256);
> - ad->res_fis = NULL;
> + if (ad->res_fis) {
> + dma_memory_unmap(ad->hba->as, ad->res_fis, 256,
> + DMA_DIRECTION_FROM_DEVICE, 256);
> + ad->res_fis = NULL;
> + }
> }
>
> static bool ahci_map_clb_address(AHCIDevice *ad)
> @@ -677,9 +679,11 @@ static bool ahci_map_clb_address(AHCIDevice *ad)
>
> static void ahci_unmap_clb_address(AHCIDevice *ad)
> {
> - dma_memory_unmap(ad->hba->as, ad->lst, 1024,
> - DMA_DIRECTION_FROM_DEVICE, 1024);
> - ad->lst = NULL;
> + if (ad->lst) {
> + dma_memory_unmap(ad->hba->as, ad->lst, 1024,
> + DMA_DIRECTION_FROM_DEVICE, 1024);
> + ad->lst = NULL;
> + }
> }
>
> static void ahci_write_fis_sdb(AHCIState *s, NCQTransferState *ncq_tfs)
>
This is fine for now as it protects us against doing something stupid in
a mechanical fashion, but I still wonder under which case we are
"starting" the FIS or CLB engines without getting a valid address. (The
unmap should only be happening when we /stop/ the engines, which implies
they were started -- which points to a bug somewhere else, too.)
Do you have a reproducer for the original issue?