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Re: [PATCH] hw/nvram/fw_cfg: fix FWCfgDataGeneratorClass::get_data() con
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [PATCH] hw/nvram/fw_cfg: fix FWCfgDataGeneratorClass::get_data() consumption |
Date: |
Fri, 18 Sep 2020 10:34:42 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 |
On 9/16/20 5:15 PM, Laszlo Ersek wrote:
> The documentation on g_byte_array_free()
> <https://developer.gnome.org/glib/stable/glib-Byte-Arrays.html#g-byte-array-free>
> says:
>
>> Returns
>>
>> the element data if free_segment is FALSE, otherwise NULL. The element
>> data should be freed using g_free().
>
> Because we currently call g_byte_array_free() with free_segment=TRUE, we
> end up passing data=NULL to fw_cfg_add_file().
>
> On the plus side, fw_cfg_data_read() and fw_cfg_dma_transfer() both deal
> with NULL data gracefully: QEMU does not crash when the guest reads such
> an item, the guest just gets a properly sized, but zero-filled blob.
>
> However, the bug breaks UEFI HTTPS boot, as the IANA_TLS_CIPHER array,
> generated otherwise correctly by the "tls-cipher-suites" object, is in
> effect replaced with a zero blob.
>
> Fix the issue by passing free_segment=FALSE to g_byte_array_free():
>
> - the caller (fw_cfg_add_from_generator()) temporarily assumes ownership
> of the generated byte array,
>
> - then ownership of the byte array is transfered to fw_cfg, as
> fw_cfg_add_file() links (not copies) "data" into fw_cfg.
>
> Cc: "Daniel P. Berrangé" <berrange@redhat.com>
> Cc: "Philippe Mathieu-Daudé" <philmd@redhat.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Fixes: 3203148917d035b09f71986ac2eaa19a352d6d9d
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> ---
> hw/nvram/fw_cfg.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
> index f3a4728288eb..0e95d057fd51 100644
> --- a/hw/nvram/fw_cfg.c
> +++ b/hw/nvram/fw_cfg.c
> @@ -1056,7 +1056,7 @@ bool fw_cfg_add_from_generator(FWCfgState *s, const
> char *filename,
> return false;
> }
> size = array->len;
> - fw_cfg_add_file(s, filename, g_byte_array_free(array, TRUE), size);
> + fw_cfg_add_file(s, filename, g_byte_array_free(array, FALSE), size);
>
> return true;
> }
>
Thanks, applied to my fw_cfg tree.