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Re: [PATCH RESEND 1/3] vfio/pci: fix a null pointer reference in vfio_ro
From: |
Alex Williamson |
Subject: |
Re: [PATCH RESEND 1/3] vfio/pci: fix a null pointer reference in vfio_rom_read |
Date: |
Mon, 24 Feb 2020 09:04:58 -0700 |
On Mon, 24 Feb 2020 14:42:17 +0800
"Longpeng(Mike)" <address@hidden> wrote:
> From: Longpeng <address@hidden>
>
> vfio_pci_load_rom() maybe failed and then the vdev->rom is NULL in
> some situation (though I've not encountered yet), maybe we should
> avoid the VM abort.
>
> Signed-off-by: Longpeng <address@hidden>
> ---
> hw/vfio/pci.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 5e75a95..ed798ae 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -768,7 +768,7 @@ static void vfio_update_msi(VFIOPCIDevice *vdev)
> }
> }
>
> -static void vfio_pci_load_rom(VFIOPCIDevice *vdev)
> +static bool vfio_pci_load_rom(VFIOPCIDevice *vdev)
> {
> struct vfio_region_info *reg_info;
> uint64_t size;
> @@ -778,7 +778,7 @@ static void vfio_pci_load_rom(VFIOPCIDevice *vdev)
> if (vfio_get_region_info(&vdev->vbasedev,
> VFIO_PCI_ROM_REGION_INDEX, ®_info)) {
> error_report("vfio: Error getting ROM info: %m");
> - return;
> + return false;
> }
>
> trace_vfio_pci_load_rom(vdev->vbasedev.name, (unsigned
> long)reg_info->size,
> @@ -797,7 +797,7 @@ static void vfio_pci_load_rom(VFIOPCIDevice *vdev)
> error_printf("Device option ROM contents are probably invalid "
> "(check dmesg).\nSkip option ROM probe with rombar=0, "
> "or load from file with romfile=\n");
> - return;
> + return false;
> }
>
> vdev->rom = g_malloc(size);
> @@ -849,6 +849,8 @@ static void vfio_pci_load_rom(VFIOPCIDevice *vdev)
> data[6] = -csum;
> }
> }
> +
> + return true;
> }
>
> static uint64_t vfio_rom_read(void *opaque, hwaddr addr, unsigned size)
> @@ -863,8 +865,9 @@ static uint64_t vfio_rom_read(void *opaque, hwaddr addr,
> unsigned size)
> uint64_t data = 0;
>
> /* Load the ROM lazily when the guest tries to read it */
> - if (unlikely(!vdev->rom && !vdev->rom_read_failed)) {
> - vfio_pci_load_rom(vdev);
> + if (unlikely(!vdev->rom && !vdev->rom_read_failed) &&
> + !vfio_pci_load_rom(vdev)) {
> + return 0;
> }
>
> memcpy(&val, vdev->rom + addr,
Looks like an obvious bug, until you look at the rest of this memcpy():
memcpy(&val, vdev->rom + addr,
(addr < vdev->rom_size) ? MIN(size, vdev->rom_size - addr) : 0);
IOW, we'll do a zero sized memcpy() if rom_size is zero, so there's no
risk of the concern identified in the commit log. This patch is
unnecessary. Thanks,
Alex