efi: Replace zero-length array and use struct_size() helper
PATCH 1/1 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")
--- drivers/firmware/efi/efi.c | 3 ++- include/linux/efi.h | 7 ++----- 2 files changed, 4 insertions(+), 6 deletions(-)
drivers/firmware/efi/efi.c +2 -1
@@ -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,
include/linux/efi.h +2 -5
@@ -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);
Signature · 1 line
2.26.2
Quoted 32 lines · 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.
Quoted 7 lines
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] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")Signed-off-by Gustavo A. R. Silva <[email protected]>
Quoted 27 lines
--- drivers/firmware/efi/efi.c | 3 ++- include/linux/efi.h | 7 ++----- 2 files changed, 4 insertions(+), 6 deletions(-)drivers/firmware/efi/efi.c +2
-1@@ -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,include/linux/efi.h +0
-0@@ -1234,14 +1234,11 @@ struct linux_efi_memreserve {struct {phys_addr_t base;phys_addr_t size;
include/linux/efi.h struct linux_efi_memreserve { · line 1241
Quoted 10 lines
include/linux/efi.h +2
-5- } 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?
Signature · 1 line
Kees Cook
Quoted 35 lines · Kees Cook
Quoted 34 lines · 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_.
Quoted 8 lines
Quoted 5 lines
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")Signed-off-by Gustavo A. R. Silva <[email protected]>Reviewed-by Kees Cook <[email protected]>
Thanks :)
Please, see more comments below...
Quoted 31 lines
Quoted 31 lines
--- drivers/firmware/efi/efi.c | 3 ++- include/linux/efi.h | 7 ++----- 2 files changed, 4 insertions(+), 6 deletions(-)drivers/firmware/efi/efi.c +2
-1@@ -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,include/linux/efi.h +1
-1@@ -1234,14 +1234,11 @@ struct linux_efi_memreserve {struct {phys_addr_t base;phys_addr_t size; - } entry[0 ]; + } entry[]; };
Quoted 10 lines
include/linux/efi.h struct linux_efi_memreserve { · line 1241
Quoted 6 lines
include/linux/efi.h +1
-4-#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
Quoted 41 lines · Gustavo A. R. Silva
Quoted 39 lines · Kees Cook
Quoted 38 lines · 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] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")
Quoted 7 lines
Quoted 4 lines
Quoted 1 line
Signed-off-by Gustavo A. R. Silva <[email protected]>Reviewed-by Kees Cook <[email protected]>Thanks :)
Queued in efi/urgent, thanks
Quoted 53 lines
Please, see more comments below...
Quoted 31 lines
Quoted 31 lines
--- drivers/firmware/efi/efi.c | 3 ++- include/linux/efi.h | 7 ++----- 2 files changed, 4 insertions(+), 6 deletions(-)drivers/firmware/efi/efi.c +2
-1@@ -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,include/linux/efi.h +1
-1@@ -1234,14 +1234,11 @@ struct linux_efi_memreserve {struct {phys_addr_t base;phys_addr_t size; - } entry[0 ]; + } entry[]; };Quoted 10 lines
include/linux/efi.h struct linux_efi_memreserve { · line 1241
Quoted 6 lines
include/linux/efi.h +1
-4-#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()andoffsetof(). I'm addressing them on the way.Thanks
--
Gustavo
The following commit has been merged into the efi/urgent branch of tip:
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 <[email protected]> AuthorDate: Wed, 27 May 2020 12:14:25 -05:00 Committer: Ard Biesheuvel <[email protected]> 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")
--- drivers/firmware/efi/efi.c | 3 ++- include/linux/efi.h | 7 ++----- 2 files changed, 4 insertions(+), 6 deletions(-)
drivers/firmware/efi/efi.c +2 -1
@@ -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,
include/linux/efi.h +2 -5
@@ -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);