6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ziyi Guo commit 405290be962b32eec842776fbe3bdf81f15b1676 upstream. access_ok() checks untagged_addr(uaddr), but arch_futex_atomic_op_inuser() and futex_atomic_cmpxchg_inatomic() hand the raw uaddr to the inline asm amoswap/amoadd/.../lr.w+sc.w through the "+m" (*uaddr) operand. When the tagged address ABI is enabled (CONFIG_RISCV_ISA_SUPM, prctl PR_SET_TAGGED_ADDR_CTRL with PMLEN != 0), those two addresses differ: a user pointer whose top PMLEN bits hold a tag passes access_ok() after untagging, but the atomic is then performed on the still-tagged raw address. Supervisor-mode data accesses are not subject to the U-mode pointer masking (that is governed by menvcfg.PMM, which the kernel does not set), so hardware does not strip the tag for the kernel's own access. With Sv57 and PMLEN=16 the tag bits overlap the canonical-address bits, so a tagged pointer can name a canonical kernel virtual address (e.g. in the linear map) whose untagged form is a valid user address. An unprivileged process can thus make FUTEX_WAKE_OP perform an atomic read-modify-write on an arbitrary kernel address, with the matching FUTEX_OP_CMP_* result serving as a read oracle. get_user()/put_user()/raw_copy_{to,from}_user() already untag the pointer after the access_ok() check; do the same in the futex helpers so the atomic operates on the address that was actually validated. Fixes: 2e1743085887 ("riscv: Add support for the tagged address ABI") Reviewed-by: Samuel Holland Signed-off-by: Ziyi Guo Link: https://patch.msgid.link/20261006140200.877263-1-guoziyi114@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Paul Walmsley Signed-off-by: Greg Kroah-Hartman --- arch/riscv/include/asm/futex.h | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/riscv/include/asm/futex.h +++ b/arch/riscv/include/asm/futex.h @@ -40,6 +40,7 @@ arch_futex_atomic_op_inuser(int op, int if (!access_ok(uaddr, sizeof(u32))) return -EFAULT; + uaddr = untagged_addr(uaddr); switch (op) { case FUTEX_OP_SET: @@ -82,6 +83,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, if (!access_ok(uaddr, sizeof(u32))) return -EFAULT; + uaddr = untagged_addr(uaddr); __enable_user_access(); __asm__ __volatile__ (