From 78004e9a87f240df03e2f73120d291763c32e0a7 Mon Sep 17 00:00:00 2001 From: Ali Ahmet Memis Date: Fri, 21 Aug 2026 01:45:27 +0000 Subject: openrisc: fix arbitrary kernel memory access via or1k_atomic syscall sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user pointers, v1 and v2, and swaps the words they point to in hand-written assembly. l.lwz r29,0(r4) l.lwz r27,0(r5) l.sw 0(r4),r27 l.sw 0(r5),r29 The pointers are not checked with access_ok(). The four memory accesses also have no exception table entries. A caller passes a kernel address as either pointer, and the syscall reads from and writes to it directly. This gives an unprivileged process a kernel read/write primitive. It overwrites kernel data such as the sys_call_table, gaining code execution in kernel context. Check both pointers before entering the critical section. Add fixups for the four memory accesses so faults on valid but unmapped user addresses return -EFAULT. [shorne@gmail.com: fix comment style] Fixes: 9d02a4283e9c ("OpenRISC: Boot code") Cc: stable@vger.kernel.org Signed-off-by: Ali Ahmet Memis Signed-off-by: Stafford Horne --- include/asm-generic/futex.h | 123 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 123 insertions(+) create mode 100644 include/asm-generic/futex.h (limited to 'include/asm-generic/futex.h') diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h new file mode 100644 index 000000000..fbbcfd801 --- /dev/null +++ b/include/asm-generic/futex.h @@ -0,0 +1,123 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_GENERIC_FUTEX_H +#define _ASM_GENERIC_FUTEX_H + +#include +#include +#include + +#ifndef futex_atomic_cmpxchg_inatomic +#ifndef CONFIG_SMP +/* + * The following implementation only for uniprocessor machines. + * It relies on preempt_disable() ensuring mutual exclusion. + * + */ +#define futex_atomic_cmpxchg_inatomic(uval, uaddr, oldval, newval) \ + futex_atomic_cmpxchg_inatomic_local(uval, uaddr, oldval, newval) +#define arch_futex_atomic_op_inuser(op, oparg, oval, uaddr) \ + futex_atomic_op_inuser_local(op, oparg, oval, uaddr) +#endif /* CONFIG_SMP */ +#endif + +/** + * futex_atomic_op_inuser_local() - Atomic arithmetic operation with constant + * argument and comparison of the previous + * futex value with another constant. + * + * @op: operation to execute + * @oparg: argument of the operation + * @oval: previous value at @uaddr on successful return + * @uaddr: pointer to user space address + * + * Return: + * 0 - On success + * -EFAULT - User access resulted in a page fault + * -EAGAIN - Atomic operation was unable to complete due to contention + * -ENOSYS - Operation not supported + */ +static inline int +futex_atomic_op_inuser_local(int op, u32 oparg, int *oval, u32 __user *uaddr) +{ + int oldval, ret; + u32 tmp; + + preempt_disable(); + + ret = -EFAULT; + if (unlikely(get_user(oldval, uaddr) != 0)) + goto out_pagefault_enable; + + ret = 0; + tmp = oldval; + + switch (op) { + case FUTEX_OP_SET: + tmp = oparg; + break; + case FUTEX_OP_ADD: + tmp += oparg; + break; + case FUTEX_OP_OR: + tmp |= oparg; + break; + case FUTEX_OP_ANDN: + tmp &= ~oparg; + break; + case FUTEX_OP_XOR: + tmp ^= oparg; + break; + default: + ret = -ENOSYS; + } + + if (ret == 0 && unlikely(put_user(tmp, uaddr) != 0)) + ret = -EFAULT; + +out_pagefault_enable: + preempt_enable(); + + if (ret == 0) + *oval = oldval; + + return ret; +} + +/** + * futex_atomic_cmpxchg_inatomic_local() - Compare and exchange the content of the + * uaddr with newval if the current value is + * oldval. + * @uval: pointer to store content of @uaddr + * @uaddr: pointer to user space address + * @oldval: old value + * @newval: new value to store to @uaddr + * + * Return: + * 0 - On success + * -EFAULT - User access resulted in a page fault + * -EAGAIN - Atomic operation was unable to complete due to contention + */ +static inline int +futex_atomic_cmpxchg_inatomic_local(u32 *uval, u32 __user *uaddr, + u32 oldval, u32 newval) +{ + u32 val; + + preempt_disable(); + if (unlikely(get_user(val, uaddr) != 0)) { + preempt_enable(); + return -EFAULT; + } + + if (val == oldval && unlikely(put_user(newval, uaddr) != 0)) { + preempt_enable(); + return -EFAULT; + } + + *uval = val; + preempt_enable(); + + return 0; +} + +#endif -- cgit v1.3.1