On 20-07-2023 14:55, Luca Vizzarro wrote:

PCuABI enablement entails providing support for userspace capability pointers which are 128-bit long instead of 64-bit.

This commit implements the support for the futex_waitv syscall while maintaining the 64-bit compatibility.

Signed-off-by: Luca Vizzarro Luca.Vizzarro@arm.com

Hello!

Sending in patch v2 for issue #48: https://git.morello-project.org/morello/kernel/linux/-/issues/48

Here you can find a branch with this patch: https://git.morello-project.org/Sevenarth/linux/-/commits/morello/futex_wait...

LTP fully passes. For the CI this fails only on the purecap tests since there has been a change in the linux headers. Therefore LTP would need to be recompiled against this for it to work.

v2 changes:

• fixes bug where the offset of the futex_waitv list was always dependent on the size of the purecap struct instead of adapting to the compat one accordingly.
• fixes the pointer cast in compat appropriately. It was mistakenly using __kernel_uintcap_t instead of __kernel_uintptr_t.

Best, Luca

---

include/uapi/linux/futex.h | 2 +- kernel/futex/syscalls.c | 32 +++++++++++++++++++++++++++++++- kernel/futex/waitwake.c | 4 ++-- 3 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/futex.h b/include/uapi/linux/futex.h index 71a5df8d2689..93f701d89401 100644 --- a/include/uapi/linux/futex.h +++ b/include/uapi/linux/futex.h @@ -63,7 +63,7 @@ */ struct futex_waitv { __u64 val;

• __u64 uaddr;

• __kernel_uintptr_t uaddr; __u32 flags; __u32 __reserved; };

diff --git a/kernel/futex/syscalls.c b/kernel/futex/syscalls.c index ad4ae797bb84..c2e4529083a3 100644 --- a/kernel/futex/syscalls.c +++ b/kernel/futex/syscalls.c @@ -190,6 +190,36 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, /* Mask of available flags for each futex in futex_waitv list */ #define FUTEXV_WAITER_MASK (FUTEX_32 | FUTEX_PRIVATE_FLAG) +struct compat_futex_waitv {

• __u64 val;
• __u64 uaddr;
• __u32 flags;
• __u32 __reserved;

+};

+static int copy_futex_waitv_from_user(struct futex_waitv *aux,

• 		      const struct futex_waitv __user *uwaitv,
  

• 		      unsigned int i)
  

+{

• if (IS_ENABLED(CONFIG_COMPAT64) && in_compat_syscall()) {

• const struct compat_futex_waitv __user *compat_uwaitv =
  

• 	(const struct compat_futex_waitv __user *)uwaitv;
  

• struct compat_futex_waitv compat_aux;
  

• if (copy_from_user(&compat_aux, &compat_uwaitv[i], sizeof(compat_aux)))
  

• 	return -EFAULT;
  

• aux->val = compat_aux.val;
  

• aux->uaddr = (__kernel_uintptr_t)compat_ptr(compat_aux.uaddr);
  

• aux->flags = compat_aux.flags;
  

• aux->__reserved = compat_aux.__reserved;
  

• return 0;
  

• }
• return copy_from_user(aux, &uwaitv[i], sizeof(*aux));

You probably want copy_from_user_with_ptr() here.

The rest looks good to me. Well done!

Tudor

+}

• /**
  • futex_parse_waitv - Parse a waitv array from userspace
  • @futexv: Kernel side list of waiters to be filled

@@ -206,7 +236,7 @@ static int futex_parse_waitv(struct futex_vector *futexv, unsigned int i; for (i = 0; i < nr_futexes; i++) {

• if (copy_from_user(&aux, &uwaitv[i], sizeof(aux)))
  

• if (copy_futex_waitv_from_user(&aux, uwaitv, i))
  return -EFAULT;
  

if ((aux.flags & ~FUTEXV_WAITER_MASK) || aux.__reserved) diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c index 1ab5640e7f84..d6b050356f81 100644 --- a/kernel/futex/waitwake.c +++ b/kernel/futex/waitwake.c @@ -422,7 +422,7 @@ static int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *wo if ((vs[i].w.flags & FUTEX_PRIVATE_FLAG) && retry) continue;

• ret = get_futex_key(u64_to_user_ptr(vs[i].w.uaddr),
  

• ret = get_futex_key((u32 __user *)vs[i].w.uaddr,
  	    !(vs[i].w.flags & FUTEX_PRIVATE_FLAG),
  	    &vs[i].q.key, FUTEX_READ);
  

@@ -433,7 +433,7 @@ static int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *wo set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE); for (i = 0; i < count; i++) {

• u32 __user *uaddr = uaddr_to_user_ptr(vs[i].w.uaddr);
  

• u32 __user *uaddr = (u32 __user *)vs[i].w.uaddr;
  

  struct futex_q *q = &vs[i].q; u32 val = (u32)vs[i].w.val;