* [PATCH] efi: Replace zero-length array and use struct_size() helper
@ 2020-05-27 17:14 Gustavo A. R. Silva
2020-05-29 8:31 ` Kees Cook
2020-06-19 16:46 ` [tip: efi/urgent] " tip-bot2 for Gustavo A. R. Silva
0 siblings, 2 replies; 5+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-27 17:14 UTC (permalink / raw)
To: Ard Biesheuvel; +Cc: linux-efi, linux-kernel, Gustavo A. R. Silva, Kees Cook
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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] efi: Replace zero-length array and use struct_size() helper
2020-05-27 17:14 [PATCH] efi: Replace zero-length array and use struct_size() helper Gustavo A. R. Silva
@ 2020-05-29 8:31 ` Kees Cook
2020-05-29 17:37 ` Gustavo A. R. Silva
2020-06-19 16:46 ` [tip: efi/urgent] " tip-bot2 for Gustavo A. R. Silva
1 sibling, 1 reply; 5+ messages in thread
From: Kees Cook @ 2020-05-29 8:31 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Ard Biesheuvel, linux-efi, linux-kernel, Gustavo A. R. Silva
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
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] efi: Replace zero-length array and use struct_size() helper
2020-05-29 8:31 ` Kees Cook
@ 2020-05-29 17:37 ` Gustavo A. R. Silva
2020-06-15 10:00 ` Ard Biesheuvel
0 siblings, 1 reply; 5+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-29 17:37 UTC (permalink / raw)
To: Kees Cook; +Cc: Ard Biesheuvel, linux-efi, linux-kernel, 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
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] efi: Replace zero-length array and use struct_size() helper
2020-05-29 17:37 ` Gustavo A. R. Silva
@ 2020-06-15 10:00 ` Ard Biesheuvel
0 siblings, 0 replies; 5+ messages in thread
From: Ard Biesheuvel @ 2020-06-15 10:00 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Kees Cook, linux-efi, Linux Kernel Mailing List, Gustavo A. R. Silva
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
^ permalink raw reply [flat|nested] 5+ messages in thread
* [tip: efi/urgent] efi: Replace zero-length array and use struct_size() helper
2020-05-27 17:14 [PATCH] efi: Replace zero-length array and use struct_size() helper Gustavo A. R. Silva
2020-05-29 8:31 ` Kees Cook
@ 2020-06-19 16:46 ` tip-bot2 for Gustavo A. R. Silva
1 sibling, 0 replies; 5+ messages in thread
From: tip-bot2 for Gustavo A. R. Silva @ 2020-06-19 16:46 UTC (permalink / raw)
To: linux-tip-commits
Cc: Gustavo A. R. Silva, Kees Cook, Ard Biesheuvel, x86, LKML
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);
^ permalink raw reply related [flat|nested] 5+ messages in thread
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2020-05-29 8:31 ` Kees Cook
2020-05-29 17:37 ` Gustavo A. R. Silva
2020-06-15 10:00 ` Ard Biesheuvel
2020-06-19 16:46 ` [tip: efi/urgent] " tip-bot2 for Gustavo A. R. Silva
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