On Thu, 14 Sep 2023 15:11:02 +0200
Clément Léger <cle...@rivosinc.com> wrote:
> enabler->uaddr can be aligned on 32 or 64 bits. If aligned on 32 bits,
> this will result in a misaligned access on 64 bits architectures since
> set_bit()/clear_bit() are expecting an unsigned long (aligned) pointer.
> On architecture that do not support misaligned access, this will crash
> the kernel. Align uaddr on unsigned long size to avoid such behavior.
> This bug was found while running kselftests on RISC-V.
>
> Fixes: 7235759084a4 ("tracing/user_events: Use remote writes for event
> enablement")
> Signed-off-by: Clément Léger <cle...@rivosinc.com>
> ---
> kernel/trace/trace_events_user.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/trace/trace_events_user.c
> b/kernel/trace/trace_events_user.c
> index 6f046650e527..580c0fe4b23e 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -479,7 +479,7 @@ static int user_event_enabler_write(struct user_event_mm
> *mm,
> bool fixup_fault, int *attempt)
> {
> unsigned long uaddr = enabler->addr;
> - unsigned long *ptr;
> + unsigned long *ptr, bit_offset;
> struct page *page;
> void *kaddr;
> int ret;
> @@ -511,13 +511,19 @@ static int user_event_enabler_write(struct
> user_event_mm *mm,
> }
>
> kaddr = kmap_local_page(page);
> +
> + bit_offset = uaddr & (sizeof(unsigned long) - 1);
> + if (bit_offset) {
> + bit_offset *= 8;
> + uaddr &= ~(sizeof(unsigned long) - 1);
> + }
> ptr = kaddr + (uaddr & ~PAGE_MASK);
>
> /* Update bit atomically, user tracers must be atomic as well */
> if (enabler->event && enabler->event->status)
> - set_bit(ENABLE_BIT(enabler), ptr);
> + set_bit(ENABLE_BIT(enabler) + bit_offset, ptr);
> else
> - clear_bit(ENABLE_BIT(enabler), ptr);
> + clear_bit(ENABLE_BIT(enabler) + bit_offset, ptr);
What we need are generic set_bit_aligned() and clear_bit_aligned(), which align
the ptr
by unsigned long. (I think it should be done in set_bit/clear_bit, for
architecture
which requires aligned access...)
#define LONG_ALIGN_DIFF(p) (p) & (sizeof(long) -1)
#define LONG_ALINGNED(p) (p) & ~(sizeof(long) - 1)
static inline void set_bit_aligned(int bit, unsigned long *ptr)
{
int offs = LONG_ALIGN_DIFF(ptr) * 8;
#ifdef __BIGENDIAN
if (bit >= offs) {
set_bit(bit - offs, LONG_ALIGNED(ptr));
} else {
set_bit(bit + BITS_PER_LONG - offs, LONG_ALIGNED(ptr) + 1);
}
#else
if (bit < BITS_PER_LONG - offs) {
set_bit(bit + offs, LONG_ALIGNED(ptr));
} else {
set_bit(bit - BITS_PER_LONG + offs, LONG_ALIGNED(ptr) + 1);
}
#endif
}
And use it.
Thank you,
>
> kunmap_local(kaddr);
> unpin_user_pages_dirty_lock(&page, 1, true);
> --
> 2.40.1
>
--
Masami Hiramatsu (Google) <mhira...@kernel.org>
