From 2963795122f50b36ed16e3ba880c3ed2de1bda6e Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Wed, 27 May 2020 12:14:25 -0500 Subject: [PATCH] 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 Reviewed-by: Kees Cook Link: https://lore.kernel.org/r/20200527171425.GA4053@embeddedor Signed-off-by: Ard Biesheuvel --- 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); -- 2.7.4