Le 06/10/2022 à 19:31, Christophe Leroy a écrit :
Le 06/10/2022 à 19:24, Jason A. Donenfeld a écrit :
Hi Christophe,
On Thu, Oct 6, 2022 at 11:21 AM Christophe Leroy
<christophe.leroy@xxxxxxxxxx> wrote:
Le 06/10/2022 à 18:53, Jason A. Donenfeld a écrit :
The prandom_u32() function has been a deprecated inline wrapper around
get_random_u32() for several releases now, and compiles down to the
exact same code. Replace the deprecated wrapper with a direct call to
the real function. The same also applies to get_random_int(), which is
just a wrapper around get_random_u32().
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Toke Høiland-Jørgensen <toke@xxxxxxx> # for sch_cake
Acked-by: Chuck Lever <chuck.lever@xxxxxxxxxx> # for nfsd
Reviewed-by: Jan Kara <jack@xxxxxxx> # for ext4
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
---
diff --git a/arch/powerpc/kernel/process.c
b/arch/powerpc/kernel/process.c
index 0fbda89cd1bb..9c4c15afbbe8 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -2308,6 +2308,6 @@ void notrace __ppc64_runlatch_off(void)
unsigned long arch_align_stack(unsigned long sp)
{
if (!(current->personality & ADDR_NO_RANDOMIZE) &&
randomize_va_space)
- sp -= get_random_int() & ~PAGE_MASK;
+ sp -= get_random_u32() & ~PAGE_MASK;
return sp & ~0xf;
Isn't that a candidate for prandom_u32_max() ?
Note that sp is deemed to be 16 bytes aligned at all time.
Yes, probably. It seemed non-trivial to think about, so I didn't. But
let's see here... maybe it's not too bad:
If PAGE_MASK is always ~(PAGE_SIZE-1), then ~PAGE_MASK is
(PAGE_SIZE-1), so prandom_u32_max(PAGE_SIZE) should yield the same
thing? Is that accurate? And holds across platforms (this comes up a
few places)? If so, I'll do that for a v4.
On powerpc it is always (from arch/powerpc/include/asm/page.h) :
/*
* Subtle: (1 << PAGE_SHIFT) is an int, not an unsigned long. So if we
* assign PAGE_MASK to a larger type it gets extended the way we want
* (i.e. with 1s in the high bits)
*/
#define PAGE_MASK (~((1 << PAGE_SHIFT) - 1))
#define PAGE_SIZE (1UL << PAGE_SHIFT)
So it would work I guess.
But taking into account that sp must remain 16 bytes aligned, would it
be better to do something like ?
sp -= prandom_u32_max(PAGE_SIZE >> 4) << 4;
return sp;
