[PATCH] efi: Replace zero-length array and use struct_size() helper

[PATCH] efi: Replace zero-length array and use struct_size() helper

[Gustavo A. R. Silva]

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][2],
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]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

Lastly, make use of the sizeof_field() helper instead of an open-coded
version.

This issue was found with the help of Coccinelle and audited _manually_.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/firmware/efi/efi.c | 3 ++-
 include/linux/efi.h        | 7 ++-----
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 7f1657b6c30df..edc5d36caf54e 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -622,7 +622,8 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables,
 			rsv = (void *)(p + prsv % PAGE_SIZE);
 
 			/* reserve the entry itself */
-			memblock_reserve(prsv, EFI_MEMRESERVE_SIZE(rsv->size));
+			memblock_reserve(prsv,
+					 struct_size(rsv, entry, rsv->size));
 
 			for (i = 0; i < atomic_read(&rsv->count); i++) {
 				memblock_reserve(rsv->entry[i].base,
diff --git a/include/linux/efi.h b/include/linux/efi.h
index c45ac969ea4eb..328cc52a5fd45 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1234,14 +1234,11 @@ struct linux_efi_memreserve {
 	struct {
 		phys_addr_t	base;
 		phys_addr_t	size;
-	} entry[0];
+	} entry[];
 };
 
-#define EFI_MEMRESERVE_SIZE(count) (sizeof(struct linux_efi_memreserve) + \
-	(count) * sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
-
 #define EFI_MEMRESERVE_COUNT(size) (((size) - sizeof(struct linux_efi_memreserve)) \
-	/ sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
+	/ sizeof_field(struct linux_efi_memreserve, entry[0]))
 
 void __init efi_arch_mem_reserve(phys_addr_t addr, u64 size);
 
-- 
2.26.2

Re: [PATCH] efi: Replace zero-length array and use struct_size() helper

[Kees Cook]

On Wed, May 27, 2020 at 12:14:25PM -0500, Gustavo A. R. Silva wrote:
> 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][2],
> 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]
> 
> sizeof(flexible-array-member) triggers a warning because flexible array
> members have incomplete type[1]. There are some instances of code in
> which the sizeof operator is being incorrectly/erroneously applied to
> zero-length arrays and the result is zero. Such instances may be hiding
> some bugs. So, this work (flexible-array member conversions) will also
> help to get completely rid of those sorts of issues.
> 
> Lastly, make use of the sizeof_field() helper instead of an open-coded
> version.
> 
> This issue was found with the help of Coccinelle and audited _manually_.
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

> ---
>  drivers/firmware/efi/efi.c | 3 ++-
>  include/linux/efi.h        | 7 ++-----
>  2 files changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 7f1657b6c30df..edc5d36caf54e 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -622,7 +622,8 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables,
>  			rsv = (void *)(p + prsv % PAGE_SIZE);
>  
>  			/* reserve the entry itself */
> -			memblock_reserve(prsv, EFI_MEMRESERVE_SIZE(rsv->size));
> +			memblock_reserve(prsv,
> +					 struct_size(rsv, entry, rsv->size));
>  
>  			for (i = 0; i < atomic_read(&rsv->count); i++) {
>  				memblock_reserve(rsv->entry[i].base,
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index c45ac969ea4eb..328cc52a5fd45 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -1234,14 +1234,11 @@ struct linux_efi_memreserve {
>  	struct {
>  		phys_addr_t	base;
>  		phys_addr_t	size;
> -	} entry[0];
> +	} entry[];
>  };
>  
> -#define EFI_MEMRESERVE_SIZE(count) (sizeof(struct linux_efi_memreserve) + \
> -	(count) * sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
> -
>  #define EFI_MEMRESERVE_COUNT(size) (((size) - sizeof(struct linux_efi_memreserve)) \
> -	/ sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
> +	/ sizeof_field(struct linux_efi_memreserve, entry[0]))

Whoa. This is kind of a "reverse struct_size()". I wonder if any other
places in the kernel do a similar calculation?

-- 
Kees Cook

Re: [PATCH] efi: Replace zero-length array and use struct_size() helper

[Gustavo A. R. Silva]

On Fri, May 29, 2020 at 01:31:54AM -0700, Kees Cook wrote:
> On Wed, May 27, 2020 at 12:14:25PM -0500, Gustavo A. R. Silva wrote:
> > 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][2],
> > 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]
> > 
> > sizeof(flexible-array-member) triggers a warning because flexible array
> > members have incomplete type[1]. There are some instances of code in
> > which the sizeof operator is being incorrectly/erroneously applied to
> > zero-length arrays and the result is zero. Such instances may be hiding
> > some bugs. So, this work (flexible-array member conversions) will also
> > help to get completely rid of those sorts of issues.
> > 
> > Lastly, make use of the sizeof_field() helper instead of an open-coded
> > version.
> > 
> > This issue was found with the help of Coccinelle and audited _manually_.
> > 
> > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> > [2] https://github.com/KSPP/linux/issues/21
> > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> > 
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> 
> Reviewed-by: Kees Cook <keescook@chromium.org>
> 

Thanks :)

Please, see more comments below...

> > ---
> >  drivers/firmware/efi/efi.c | 3 ++-
> >  include/linux/efi.h        | 7 ++-----
> >  2 files changed, 4 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> > index 7f1657b6c30df..edc5d36caf54e 100644
> > --- a/drivers/firmware/efi/efi.c
> > +++ b/drivers/firmware/efi/efi.c
> > @@ -622,7 +622,8 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables,
> >  			rsv = (void *)(p + prsv % PAGE_SIZE);
> >  
> >  			/* reserve the entry itself */
> > -			memblock_reserve(prsv, EFI_MEMRESERVE_SIZE(rsv->size));
> > +			memblock_reserve(prsv,
> > +					 struct_size(rsv, entry, rsv->size));
> >  
> >  			for (i = 0; i < atomic_read(&rsv->count); i++) {
> >  				memblock_reserve(rsv->entry[i].base,
> > diff --git a/include/linux/efi.h b/include/linux/efi.h
> > index c45ac969ea4eb..328cc52a5fd45 100644
> > --- a/include/linux/efi.h
> > +++ b/include/linux/efi.h
> > @@ -1234,14 +1234,11 @@ struct linux_efi_memreserve {
> >  	struct {
> >  		phys_addr_t	base;
> >  		phys_addr_t	size;
> > -	} entry[0];
> > +	} entry[];
> >  };
> >  
> > -#define EFI_MEMRESERVE_SIZE(count) (sizeof(struct linux_efi_memreserve) + \
> > -	(count) * sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
> > -
> >  #define EFI_MEMRESERVE_COUNT(size) (((size) - sizeof(struct linux_efi_memreserve)) \
> > -	/ sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
> > +	/ sizeof_field(struct linux_efi_memreserve, entry[0]))
> 
> Whoa. This is kind of a "reverse struct_size()". I wonder if any other
> places in the kernel do a similar calculation?
> 

So far this is the only intance of this I've run into. 

What I've found is that there are many instances of the open-coded
version of sizeof_field() and offsetof(). I'm addressing them on the
way.

Thanks
--
Gustavo

Re: [PATCH] efi: Replace zero-length array and use struct_size() helper

[Ard Biesheuvel]

On Fri, 29 May 2020 at 19:32, Gustavo A. R. Silva <gustavoars@kernel.org> wrote:
>
> On Fri, May 29, 2020 at 01:31:54AM -0700, Kees Cook wrote:
> > On Wed, May 27, 2020 at 12:14:25PM -0500, Gustavo A. R. Silva wrote:
> > > 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][2],
> > > 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]
> > >
> > > sizeof(flexible-array-member) triggers a warning because flexible array
> > > members have incomplete type[1]. There are some instances of code in
> > > which the sizeof operator is being incorrectly/erroneously applied to
> > > zero-length arrays and the result is zero. Such instances may be hiding
> > > some bugs. So, this work (flexible-array member conversions) will also
> > > help to get completely rid of those sorts of issues.
> > >
> > > Lastly, make use of the sizeof_field() helper instead of an open-coded
> > > version.
> > >
> > > This issue was found with the help of Coccinelle and audited _manually_.
> > >
> > > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> > > [2] https://github.com/KSPP/linux/issues/21
> > > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> > >
> > > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> >
> > Reviewed-by: Kees Cook <keescook@chromium.org>
> >
>
> Thanks :)
>

Queued in efi/urgent, thanks


> Please, see more comments below...
>
> > > ---
> > >  drivers/firmware/efi/efi.c | 3 ++-
> > >  include/linux/efi.h        | 7 ++-----
> > >  2 files changed, 4 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> > > index 7f1657b6c30df..edc5d36caf54e 100644
> > > --- a/drivers/firmware/efi/efi.c
> > > +++ b/drivers/firmware/efi/efi.c
> > > @@ -622,7 +622,8 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables,
> > >                     rsv = (void *)(p + prsv % PAGE_SIZE);
> > >
> > >                     /* reserve the entry itself */
> > > -                   memblock_reserve(prsv, EFI_MEMRESERVE_SIZE(rsv->size));
> > > +                   memblock_reserve(prsv,
> > > +                                    struct_size(rsv, entry, rsv->size));
> > >
> > >                     for (i = 0; i < atomic_read(&rsv->count); i++) {
> > >                             memblock_reserve(rsv->entry[i].base,
> > > diff --git a/include/linux/efi.h b/include/linux/efi.h
> > > index c45ac969ea4eb..328cc52a5fd45 100644
> > > --- a/include/linux/efi.h
> > > +++ b/include/linux/efi.h
> > > @@ -1234,14 +1234,11 @@ struct linux_efi_memreserve {
> > >     struct {
> > >             phys_addr_t     base;
> > >             phys_addr_t     size;
> > > -   } entry[0];
> > > +   } entry[];
> > >  };
> > >
> > > -#define EFI_MEMRESERVE_SIZE(count) (sizeof(struct linux_efi_memreserve) + \
> > > -   (count) * sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
> > > -
> > >  #define EFI_MEMRESERVE_COUNT(size) (((size) - sizeof(struct linux_efi_memreserve)) \
> > > -   / sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
> > > +   / sizeof_field(struct linux_efi_memreserve, entry[0]))
> >
> > Whoa. This is kind of a "reverse struct_size()". I wonder if any other
> > places in the kernel do a similar calculation?
> >
>
> So far this is the only intance of this I've run into.
>
> What I've found is that there are many instances of the open-coded
> version of sizeof_field() and offsetof(). I'm addressing them on the
> way.
>
> Thanks
> --
> Gustavo

[tip: efi/urgent] efi: Replace zero-length array and use struct_size() helper

[tip-bot2 for Gustavo A. R. Silva]

The following commit has been merged into the efi/urgent branch of tip:

Commit-ID:     2963795122f50b36ed16e3ba880c3ed2de1bda6e
Gitweb:        https://git.kernel.org/tip/2963795122f50b36ed16e3ba880c3ed2de1bda6e
Author:        Gustavo A. R. Silva <gustavoars@kernel.org>
AuthorDate:    Wed, 27 May 2020 12:14:25 -05:00
Committer:     Ard Biesheuvel <ardb@kernel.org>
CommitterDate: Mon, 15 Jun 2020 14:38:56 +02:00

efi: Replace zero-length array and use struct_size() helper

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][2],
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]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

Lastly, make use of the sizeof_field() helper instead of an open-coded
version.

This issue was found with the help of Coccinelle and audited _manually_.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200527171425.GA4053@embeddedor
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/efi/efi.c | 3 ++-
 include/linux/efi.h        | 7 ++-----
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 7f1657b..edc5d36 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -622,7 +622,8 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables,
 			rsv = (void *)(p + prsv % PAGE_SIZE);
 
 			/* reserve the entry itself */
-			memblock_reserve(prsv, EFI_MEMRESERVE_SIZE(rsv->size));
+			memblock_reserve(prsv,
+					 struct_size(rsv, entry, rsv->size));
 
 			for (i = 0; i < atomic_read(&rsv->count); i++) {
 				memblock_reserve(rsv->entry[i].base,
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 2c6495f..c3449c9 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1236,14 +1236,11 @@ struct linux_efi_memreserve {
 	struct {
 		phys_addr_t	base;
 		phys_addr_t	size;
-	} entry[0];
+	} entry[];
 };
 
-#define EFI_MEMRESERVE_SIZE(count) (sizeof(struct linux_efi_memreserve) + \
-	(count) * sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
-
 #define EFI_MEMRESERVE_COUNT(size) (((size) - sizeof(struct linux_efi_memreserve)) \
-	/ sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
+	/ sizeof_field(struct linux_efi_memreserve, entry[0]))
 
 void __init efi_arch_mem_reserve(phys_addr_t addr, u64 size);