Messages in this thread | | | Date | Sun, 17 Sep 2023 16:10:59 +0200 | Subject | Re: [PATCH] tracing/user_events: align uaddr on unsigned long alignment | From | Clément Léger <> |
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On 15/09/2023 04:54, Masami Hiramatsu (Google) wrote: > On Thu, 14 Sep 2023 15:11:02 +0200 > Clément Léger <cleger@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 <cleger@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 > }
Hi Masami,
Indeed, that is a more elegant version, thanks for the snippet.
Clément
> > And use it. > > Thank you, > >> >> kunmap_local(kaddr); >> unpin_user_pages_dirty_lock(&page, 1, true); >> -- >> 2.40.1 >> > >
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