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Re: [Xen-devel] [PATCH] x86/boot: Fix latent memory corruption with early_boot_opts_t
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 2 May 2019 14:33:11 +0100
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- Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 02 May 2019 13:33:22 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 02/05/2019 13:44, Jan Beulich wrote:
>>>> On 02.05.19 at 13:52, <andrew.cooper3@xxxxxxxxxx> wrote:
>> c/s ebb26b509f "xen/x86: make VGA support selectable" added an #ifdef
>> CONFIG_VIDEO into the middle the backing space for early_boot_opts_t,
>> but didn't adjust the structure definition in cmdline.c
>>
>> This only functions correctly because the affected fields are at the end
>> of the structure, and cmdline.c doesn't write to them in this case.
>>
>> To retain the slimming effect of compiling out CONFIG_VIDEO, adjust
>> cmdline.c with enough #ifdef-ary to make C's idea of the structure match
>> the declaration in asm. This requires adding __maybe_unused annotations
>> to two helper functions.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> with a remark and a question:
>
>> --- a/xen/arch/x86/boot/cmdline.c
>> +++ b/xen/arch/x86/boot/cmdline.c
>> @@ -40,10 +40,12 @@ typedef struct __packed {
>> u8 opt_edd;
>> u8 opt_edid;
>> u8 padding;
>> +#ifdef CONFIG_VIDEO
>> u16 boot_vid_mode;
>> u16 vesa_width;
>> u16 vesa_height;
>> u16 vesa_depth;
>> +#endif
> Since apparently the "Keep in sync" comment in trampoline.S
> wasn't sufficient, and since - with what said commit did - the
> comment now looks unrelated to these data items (for there
> being a blank line in between now) perhaps this should be
> accompanied by both a START and END marker?
I've got a followup patch which cleans up the ASM, but I don't want to
interfere with the work that David is currently preparing.
> And perhaps the comment next to vesa_size should also
> get corrected to say "width x height x depth".
I had already addressed this, and the fact that boot_vid_mode has never
needed to be global (ever since its introduction).
>
>> --- a/xen/arch/x86/boot/defs.h
>> +++ b/xen/arch/x86/boot/defs.h
>> @@ -23,6 +23,7 @@
>> #include "../../../include/xen/stdbool.h"
>>
>> #define __packed __attribute__((__packed__))
>> +#define __maybe_unused __attribute__((__unused__))
>> #define __stdcall __attribute__((__stdcall__))
> Purely out of curiosity (I don't really care about the ordering
> here as long as the set doesn't meaningfully grow): Based on
> what did you decide this best goes between the two existing
> ones?
I forgot to sort the lines. Fixed.
~Andrew
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