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powerpc: Use correct procedure call standard for getrandom vDSO call (bug 32440)

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A plain indirect function call does not work on POWER because
success and failure are signaled through a flag register, and
not via the usual Linux negative return value convention.

This has potential security impact, in two ways: the return value
could be out of bounds (EAGAIN is 11 on powerpc6le), and no
random bytes have been written despite the non-error return value.

Fixes commit 461cab1de7 ("linux: Add
support for getrandom vDSO").

Reported-by: Ján Stanček <jstancek@redhat.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Florian Weimer
2024-12-10 16:17:06 +01:00
parent b79f257533
commit 4f5704ea34
3 changed files with 49 additions and 6 deletions
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17
sysdeps/unix/sysv/linux/getrandom.c
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@ -20,6 +20,8 @@
#include <errno.h>
#include <unistd.h>
#include <sysdep-cancel.h>
#include <sysdep.h>
#include <sysdep-vdso.h>
static inline ssize_t
getrandom_syscall (void *buffer, size_t length, unsigned int flags,
@ -201,11 +203,12 @@ getrandom_vdso (void *buffer, size_t length, unsigned int flags, bool cancel)
cancellation bridge (__syscall_cancel_arch), use GRND_NONBLOCK so there
is no potential unbounded blocking in the kernel. It should be a rare
situation, only at system startup when RNG is not initialized. */
ssize_t ret = GLRO (dl_vdso_getrandom) (buffer,
length,
flags | GRND_NONBLOCK,
state,
state_size);
long int ret = INTERNAL_VSYSCALL_CALL (GLRO (dl_vdso_getrandom), 5,
buffer,
length,
flags | GRND_NONBLOCK,
state,
state_size);
if (INTERNAL_SYSCALL_ERROR_P (ret))
{
/* Fallback to the syscall if the kernel would block. */
@ -241,7 +244,9 @@ __getrandom_early_init (_Bool initial)
uint32_t mmap_flags;
uint32_t reserved[13];
} params;
if (GLRO(dl_vdso_getrandom) (NULL, 0, 0, &params, ~0UL) == 0)
long int ret = INTERNAL_VSYSCALL_CALL (GLRO(dl_vdso_getrandom),
5, NULL, 0, 0, &params, ~0UL);
if (! INTERNAL_SYSCALL_ERROR_P (ret))
{
/* Align each opaque state to L1 data cache size to avoid false
sharing. If the size can not be obtained, use the kernel