Re: [PATCH] Avoid crash calling PrintErrMesg from efi_multiboot2

[Frediano Ziglio <frediano.ziglio@xxxxxxxxx>]

On Mon, Aug 19, 2024 at 12:35 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 19.08.2024 13:07, Frediano Ziglio wrote:
> > --- a/xen/common/efi/boot.c
> > +++ b/xen/common/efi/boot.c
> > @@ -287,19 +287,36 @@ static bool __init match_guid(const EFI_GUID *guid1, 
> > const EFI_GUID *guid2)
> >  /* generic routine for printing error messages */
> >  static void __init PrintErrMesg(const CHAR16 *mesg, EFI_STATUS ErrCode)
> >  {
> > -    static const CHAR16* const ErrCodeToStr[] __initconstrel = {
> > -        [~EFI_ERROR_MASK & EFI_NOT_FOUND]           = L"Not found",
> > -        [~EFI_ERROR_MASK & EFI_NO_MEDIA]            = L"The device has no 
> > media",
> > -        [~EFI_ERROR_MASK & EFI_MEDIA_CHANGED]       = L"Media changed",
> > -        [~EFI_ERROR_MASK & EFI_DEVICE_ERROR]        = L"Device error",
> > -        [~EFI_ERROR_MASK & EFI_VOLUME_CORRUPTED]    = L"Volume corrupted",
> > -        [~EFI_ERROR_MASK & EFI_ACCESS_DENIED]       = L"Access denied",
> > -        [~EFI_ERROR_MASK & EFI_OUT_OF_RESOURCES]    = L"Out of resources",
> > -        [~EFI_ERROR_MASK & EFI_VOLUME_FULL]         = L"Volume is full",
> > -        [~EFI_ERROR_MASK & EFI_SECURITY_VIOLATION]  = L"Security 
> > violation",
> > -        [~EFI_ERROR_MASK & EFI_CRC_ERROR]           = L"CRC error",
> > -        [~EFI_ERROR_MASK & EFI_COMPROMISED_DATA]    = L"Compromised data",
> > -        [~EFI_ERROR_MASK & EFI_BUFFER_TOO_SMALL]    = L"Buffer too small",
> > +#define ERROR_MESSAGE_LIST \
> > +    ERROR_MESSAGE(EFI_NOT_FOUND, "Not found") \
> > +    ERROR_MESSAGE(EFI_NO_MEDIA, "The device has no media") \
> > +    ERROR_MESSAGE(EFI_MEDIA_CHANGED, "Media changed") \
> > +    ERROR_MESSAGE(EFI_DEVICE_ERROR, "Device error") \
> > +    ERROR_MESSAGE(EFI_VOLUME_CORRUPTED, "Volume corrupted") \
> > +    ERROR_MESSAGE(EFI_ACCESS_DENIED, "Access denied") \
> > +    ERROR_MESSAGE(EFI_OUT_OF_RESOURCES, "Out of resources") \
> > +    ERROR_MESSAGE(EFI_VOLUME_FULL, "Volume is full") \
> > +    ERROR_MESSAGE(EFI_SECURITY_VIOLATION, "Security violation") \
> > +    ERROR_MESSAGE(EFI_CRC_ERROR, "CRC error") \
> > +    ERROR_MESSAGE(EFI_COMPROMISED_DATA, "Compromised data") \
> > +    ERROR_MESSAGE(EFI_BUFFER_TOO_SMALL, "Buffer too small")
> > +
> > +    static const struct ErrorStrings {
>
> __initconst?
>

It's below, attached to the variable, it cannot be attached to a
structure declaration.

> > +        CHAR16 start;
> > +#undef ERROR_MESSAGE
> > +#define ERROR_MESSAGE(code, str) CHAR16 msg_ ## code[sizeof(str)];
> > +        ERROR_MESSAGE_LIST
> > +    } ErrorStrings __initconst = {

Here it is.

> > +        0
> > +#undef ERROR_MESSAGE
> > +#define ERROR_MESSAGE(code, str) , L ## str
> > +        ERROR_MESSAGE_LIST
> > +    };
> > +    static const uint16_t ErrCodeToStr[] __initconst = {
> > +#undef ERROR_MESSAGE
> > +#define ERROR_MESSAGE(code, str) \
> > +        [~EFI_ERROR_MASK & code] = offsetof(struct ErrorStrings, msg_ ## 
> > code),
> > +        ERROR_MESSAGE_LIST
> >      };
> >      EFI_STATUS ErrIdx = ErrCode & ~EFI_ERROR_MASK;
> >
> > @@ -308,7 +325,7 @@ static void __init PrintErrMesg(const CHAR16 *mesg, 
> > EFI_STATUS ErrCode)
> >      PrintErr(L": ");
> >
> >      if( (ErrIdx < ARRAY_SIZE(ErrCodeToStr)) && ErrCodeToStr[ErrIdx] )
> > -        mesg = ErrCodeToStr[ErrIdx];
> > +        mesg = (CHAR16*) ((char*) &ErrorStrings + ErrCodeToStr[ErrIdx]);
>
> Please never cast away const. Also (nit) please put the blanks at the right
> places. Finally instead of casting to char * (something string-like)
> intermediately, perhaps better cast to void *? Taken together
>
>         mesg = (const CHAR16 *)((const void *)&ErrorStrings + 
> ErrCodeToStr[ErrIdx]);
>

Done, less portable but it's not portable code.

> (which looks like it'll then also need line-wrapping).
>
> Further please add an appropriate Fixes: tag.
>

Done

> Jan

Frediano