[SeaBIOS] [PATCH] std/tcg: Replace zero-length array with flexible-array member

Paul Menzel posted 1 patch 19 weeks ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/seabios tags/patchew/1b697e9f-842e-2000-798d-584a1c4c52b9@molgen.mpg.de
src/std/tcg.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

[SeaBIOS] [PATCH] std/tcg: Replace zero-length array with flexible-array member

Posted by Paul Menzel 19 weeks ago
Date: Tue, 3 Mar 2020 16:24:46 +0100

GCC 10 gives the warnings below:

    In file included from out/ccode32flat.o.tmp.c:54:
    ./src/tcgbios.c: In function 'tpm20_write_EfiSpecIdEventStruct':
    ./src/tcgbios.c:290:30: warning: array subscript '(<unknown>) + 4294967295' is outside the bounds of an interior zero-length array 'struct TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
      290 |         event.hdr.digestSizes[count].algorithmId = be16_to_cpu(sel->hashAlg);
          |         ~~~~~~~~~~~~~~~~~~~~~^~~~~~~
    In file included from ./src/tcgbios.c:22,
                     from out/ccode32flat.o.tmp.c:54:
    ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
      527 |     } digestSizes[0];
          |       ^~~~~~~~~~~
    In file included from out/ccode32flat.o.tmp.c:54:
    ./src/tcgbios.c:291:30: warning: array subscript '(<unknown>) + 4294967295' is outside the bounds of an interior zero-length array 'struct TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
      291 |         event.hdr.digestSizes[count].digestSize = hsize;
          |         ~~~~~~~~~~~~~~~~~~~~~^~~~~~~
    In file included from ./src/tcgbios.c:22,
                     from out/ccode32flat.o.tmp.c:54:
    ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
      527 |     } digestSizes[0];
          |       ^~~~~~~~~~~

[Description copied from Gustavo A. R. Silva <gustavo@embeddedor.com>
from his Linux kernel commits.]

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array
member [1], introduced in C99:

    struct foo {
            int stuff;
            struct boo array[];
    };

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html

Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
---
 src/std/tcg.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/std/tcg.h b/src/std/tcg.h
index 1cc1c92..1c9eeb4 100644
--- a/src/std/tcg.h
+++ b/src/std/tcg.h
@@ -524,7 +524,7 @@ struct TCG_EfiSpecIdEventStruct {
     struct TCG_EfiSpecIdEventAlgorithmSize {
         u16 algorithmId;
         u16 digestSize;
-    } digestSizes[0];
+    } digestSizes[];
     /*
     u8 vendorInfoSize;
     u8 vendorInfo[0];
-- 
2.25.0

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[SeaBIOS] Re: [PATCH] std/tcg: Replace zero-length array with flexible-array member

Posted by Stefan Berger 18 weeks ago
On 3/3/20 11:50 AM, Paul Menzel wrote:
> Date: Tue, 3 Mar 2020 16:24:46 +0100
>
> GCC 10 gives the warnings below:
>
>      In file included from out/ccode32flat.o.tmp.c:54:
>      ./src/tcgbios.c: In function 'tpm20_write_EfiSpecIdEventStruct':
>      ./src/tcgbios.c:290:30: warning: array subscript '(<unknown>) + 4294967295' is outside the bounds of an interior zero-length array 'struct TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
>        290 |         event.hdr.digestSizes[count].algorithmId = be16_to_cpu(sel->hashAlg);
>            |         ~~~~~~~~~~~~~~~~~~~~~^~~~~~~
>      In file included from ./src/tcgbios.c:22,
>                       from out/ccode32flat.o.tmp.c:54:
>      ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
>        527 |     } digestSizes[0];
>            |       ^~~~~~~~~~~
>      In file included from out/ccode32flat.o.tmp.c:54:
>      ./src/tcgbios.c:291:30: warning: array subscript '(<unknown>) + 4294967295' is outside the bounds of an interior zero-length array 'struct TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
>        291 |         event.hdr.digestSizes[count].digestSize = hsize;
>            |         ~~~~~~~~~~~~~~~~~~~~~^~~~~~~
>      In file included from ./src/tcgbios.c:22,
>                       from out/ccode32flat.o.tmp.c:54:
>      ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
>        527 |     } digestSizes[0];
>            |       ^~~~~~~~~~~
>
> [Description copied from Gustavo A. R. Silva <gustavo@embeddedor.com>
> from his Linux kernel commits.]
>
> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array
> member [1], introduced in C99:
>
>      struct foo {
>              int stuff;
>              struct boo array[];
>      };
>
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertently introduced[3] to the codebase from now on.
>
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
>
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
>
> This issue was found with the help of Coccinelle.
>
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
>
> Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>

It gives the same size of structure either way.

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>


> ---
>   src/std/tcg.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/std/tcg.h b/src/std/tcg.h
> index 1cc1c92..1c9eeb4 100644
> --- a/src/std/tcg.h
> +++ b/src/std/tcg.h
> @@ -524,7 +524,7 @@ struct TCG_EfiSpecIdEventStruct {
>       struct TCG_EfiSpecIdEventAlgorithmSize {
>           u16 algorithmId;
>           u16 digestSize;
> -    } digestSizes[0];
> +    } digestSizes[];
>       /*
>       u8 vendorInfoSize;
>       u8 vendorInfo[0];
>
> _______________________________________________
> SeaBIOS mailing list -- seabios@seabios.org
> To unsubscribe send an email to seabios-leave@seabios.org


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[SeaBIOS] Re: [PATCH] std/tcg: Replace zero-length array with flexible-array member

Posted by Philippe Mathieu-Daudé 19 weeks ago
Hello Paul,

On 3/3/20 5:50 PM, Paul Menzel wrote:
> Date: Tue, 3 Mar 2020 16:24:46 +0100
> 
> GCC 10 gives the warnings below:
> 
>      In file included from out/ccode32flat.o.tmp.c:54:
>      ./src/tcgbios.c: In function 'tpm20_write_EfiSpecIdEventStruct':
>      ./src/tcgbios.c:290:30: warning: array subscript '(<unknown>) + 4294967295' is outside the bounds of an interior zero-length array 'struct TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
>        290 |         event.hdr.digestSizes[count].algorithmId = be16_to_cpu(sel->hashAlg);
>            |         ~~~~~~~~~~~~~~~~~~~~~^~~~~~~
>      In file included from ./src/tcgbios.c:22,
>                       from out/ccode32flat.o.tmp.c:54:
>      ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
>        527 |     } digestSizes[0];
>            |       ^~~~~~~~~~~
>      In file included from out/ccode32flat.o.tmp.c:54:
>      ./src/tcgbios.c:291:30: warning: array subscript '(<unknown>) + 4294967295' is outside the bounds of an interior zero-length array 'struct TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
>        291 |         event.hdr.digestSizes[count].digestSize = hsize;
>            |         ~~~~~~~~~~~~~~~~~~~~~^~~~~~~
>      In file included from ./src/tcgbios.c:22,
>                       from out/ccode32flat.o.tmp.c:54:
>      ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
>        527 |     } digestSizes[0];
>            |       ^~~~~~~~~~~
> 
> [Description copied from Gustavo A. R. Silva <gustavo@embeddedor.com>
> from his Linux kernel commits.]
> 
> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array
> member [1], introduced in C99:
> 
>      struct foo {
>              int stuff;
>              struct boo array[];
>      };
> 
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertently introduced[3] to the codebase from now on.

Assuming this comment is also part of the Linux kernel commit, can we 
drop the '[3]' marker?

> 
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
> 
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
> 
> This issue was found with the help of Coccinelle.
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> 
> Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
> ---
>   src/std/tcg.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/std/tcg.h b/src/std/tcg.h
> index 1cc1c92..1c9eeb4 100644
> --- a/src/std/tcg.h
> +++ b/src/std/tcg.h
> @@ -524,7 +524,7 @@ struct TCG_EfiSpecIdEventStruct {
>       struct TCG_EfiSpecIdEventAlgorithmSize {
>           u16 algorithmId;
>           u16 digestSize;
> -    } digestSizes[0];
> +    } digestSizes[];
>       /*
>       u8 vendorInfoSize;
>       u8 vendorInfo[0];
> 
> 
> _______________________________________________
> SeaBIOS mailing list -- seabios@seabios.org
> To unsubscribe send an email to seabios-leave@seabios.org
> 
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[SeaBIOS] Re: [PATCH] std/tcg: Replace zero-length array with flexible-array member

Posted by Philippe Mathieu-Daudé 19 weeks ago
On Tue, Mar 3, 2020 at 7:08 PM Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
>
> Hello Paul,
>
> On 3/3/20 5:50 PM, Paul Menzel wrote:
> > Date: Tue, 3 Mar 2020 16:24:46 +0100
> >
> > GCC 10 gives the warnings below:
> >
> >      In file included from out/ccode32flat.o.tmp.c:54:
> >      ./src/tcgbios.c: In function 'tpm20_write_EfiSpecIdEventStruct':
> >      ./src/tcgbios.c:290:30: warning: array subscript '(<unknown>) + 4294967295' is outside the bounds of an interior zero-length array 'struct TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
> >        290 |         event.hdr.digestSizes[count].algorithmId = be16_to_cpu(sel->hashAlg);
> >            |         ~~~~~~~~~~~~~~~~~~~~~^~~~~~~
> >      In file included from ./src/tcgbios.c:22,
> >                       from out/ccode32flat.o.tmp.c:54:
> >      ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
> >        527 |     } digestSizes[0];
> >            |       ^~~~~~~~~~~
> >      In file included from out/ccode32flat.o.tmp.c:54:
> >      ./src/tcgbios.c:291:30: warning: array subscript '(<unknown>) + 4294967295' is outside the bounds of an interior zero-length array 'struct TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
> >        291 |         event.hdr.digestSizes[count].digestSize = hsize;
> >            |         ~~~~~~~~~~~~~~~~~~~~~^~~~~~~
> >      In file included from ./src/tcgbios.c:22,
> >                       from out/ccode32flat.o.tmp.c:54:
> >      ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
> >        527 |     } digestSizes[0];
> >            |       ^~~~~~~~~~~
> >
> > [Description copied from Gustavo A. R. Silva <gustavo@embeddedor.com>
> > from his Linux kernel commits.]
> >
> > The current codebase makes use of the zero-length array language
> > extension to the C90 standard, but the preferred mechanism to declare
> > variable-length types such as these ones is a flexible array
> > member [1], introduced in C99:
> >
> >      struct foo {
> >              int stuff;
> >              struct boo array[];
> >      };
> >
> > By making use of the mechanism above, we will get a compiler warning
> > in case the flexible array does not occur last in the structure, which
> > will help us prevent some kind of undefined behavior bugs from being
> > inadvertently introduced[3] to the codebase from now on.
>
> Assuming this comment is also part of the Linux kernel commit, can we
> drop the '[3]' marker?

Assuming the maintainer can do this trivial change:
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

>
> >
> > Also, notice that, dynamic memory allocations won't be affected by
> > this change:
> >
> > "Flexible array members have incomplete type, and so the sizeof operator
> > may not be applied. As a quirk of the original implementation of
> > zero-length arrays, sizeof evaluates to zero."[1]
> >
> > This issue was found with the help of Coccinelle.
> >
> > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> >
> > Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
> > ---
> >   src/std/tcg.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/src/std/tcg.h b/src/std/tcg.h
> > index 1cc1c92..1c9eeb4 100644
> > --- a/src/std/tcg.h
> > +++ b/src/std/tcg.h
> > @@ -524,7 +524,7 @@ struct TCG_EfiSpecIdEventStruct {
> >       struct TCG_EfiSpecIdEventAlgorithmSize {
> >           u16 algorithmId;
> >           u16 digestSize;
> > -    } digestSizes[0];
> > +    } digestSizes[];
> >       /*
> >       u8 vendorInfoSize;
> >       u8 vendorInfo[0];
> >
> >
> > _______________________________________________
> > SeaBIOS mailing list -- seabios@seabios.org
> > To unsubscribe send an email to seabios-leave@seabios.org
> >
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