@@ -219,6 +219,14 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
p = arch_align_stack(p);
+ /*
+ * Generate 16 random bytes for userspace PRNG seeding.
+ */
+ get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes));
+ u_rand_bytes = elf_stack_alloc(&p, sizeof(k_rand_bytes));
+ if (__copy_to_user(u_rand_bytes, k_rand_bytes, sizeof(k_rand_bytes)))
+ return -EFAULT;
+
/*
* If this architecture has a platform capability string, copy it
* to userspace. In some cases (Sparc), this info is impossible
@@ -247,14 +255,6 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
return -EFAULT;
}
- /*
- * Generate 16 random bytes for userspace PRNG seeding.
- */
- get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes));
- u_rand_bytes = elf_stack_alloc(&p, sizeof(k_rand_bytes));
- if (__copy_to_user(u_rand_bytes, k_rand_bytes, sizeof(k_rand_bytes)))
- return -EFAULT;
-
/* Create the ELF interpreter info */
elf_info = (elf_addr_t *)current->mm->saved_auxv;
/* update AT_VECTOR_SIZE_BASE if the number of NEW_AUX_ENT() changes */
Because AT_RANDOM array is put on stack after AT_PLATFORM and AT_BASE_PLATFORM strings, it's aligned on a 1 byte boundary: on x86: $ for i in 1 2 3 ; do LD_SHOW_AUXV=1 ./bin32 | grep AT_RANDOM ; done AT_RANDOM: 0xffb91ffb AT_RANDOM: 0xffcd60eb AT_RANDOM: 0xffd7d99b on x86_64: $ for i in 1 2 3 ; do LD_SHOW_AUXV=1 ./bin64 | grep AT_RANDOM ; done AT_RANDOM: 0x7ffe3ce7d559 AT_RANDOM: 0x7ffeb9ecd2b9 AT_RANDOM: 0x7ffd37cebd49 Unlike AT_ENTROPY1 and AT_ENTROPY2, AT_ENTROPY, or AT_RANDOM1 and AT_RANDOM2 proposals[1][2][3] which would be 32bits or 64bits integers, kernel never promise AT_RANDOM array to be aligned[4]. But having a 16bytes array not aligned might not be optimal. Userspace could benefit from an aligned array. As the AT_PLATFORM and AT_BASE_PLATFORM are asciiz C strings, they don't need to be aligned, thus they can be put after AT_RANDOM array. As AT_RANDOM array is first put on stack, it's alignment should match the one set by arch_align_stack(). [1] https://lore.kernel.org/lkml/4675C678.3080807@gentoo.org/ [2] https://lore.kernel.org/lkml/467948F5.3010709@gentoo.org/ [3] https://sourceware.org/ml/libc-alpha/2008-10/msg00013.html [1] https://lore.kernel.org/lkml/20081003001616.GN10632@outflux.net/ Link: https://lore.kernel.org/lkml/cover.1560423331.git.ydroneaud@opteya.com Signed-off-by: Yann Droneaud <ydroneaud@opteya.com> --- fs/binfmt_elf.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)