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/rwonce.h | 98 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 98 insertions(+) create mode 100644 include/asm-generic/rwonce.h (limited to 'include/asm-generic/rwonce.h') diff --git a/include/asm-generic/rwonce.h b/include/asm-generic/rwonce.h new file mode 100644 index 000000000..52b969c7c --- /dev/null +++ b/include/asm-generic/rwonce.h @@ -0,0 +1,98 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Prevent the compiler from merging or refetching reads or writes. The + * compiler is also forbidden from reordering successive instances of + * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some + * particular ordering. One way to make the compiler aware of ordering is to + * put the two invocations of READ_ONCE or WRITE_ONCE in different C + * statements. + * + * These two macros will also work on aggregate data types like structs or + * unions. + * + * Their two major use cases are: (1) Mediating communication between + * process-level code and irq/NMI handlers, all running on the same CPU, + * and (2) Ensuring that the compiler does not fold, spindle, or otherwise + * mutilate accesses that either do not require ordering or that interact + * with an explicit memory barrier or atomic instruction that provides the + * required ordering. + */ +#ifndef __ASM_GENERIC_RWONCE_H +#define __ASM_GENERIC_RWONCE_H + +#ifndef __ASSEMBLY__ + +#include +#include +#include + +/* + * Yes, this permits 64-bit accesses on 32-bit architectures. These will + * actually be atomic in some cases (namely Armv7 + LPAE), but for others we + * rely on the access being split into 2x32-bit accesses for a 32-bit quantity + * (e.g. a virtual address) and a strong prevailing wind. + */ +#define compiletime_assert_rwonce_type(t) \ + compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \ + "Unsupported access size for {READ,WRITE}_ONCE().") + +/* + * Use __READ_ONCE() instead of READ_ONCE() if you do not require any + * atomicity. Note that this may result in tears! + */ +#ifndef __READ_ONCE +#define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x)) +#endif + +#define READ_ONCE(x) \ +({ \ + compiletime_assert_rwonce_type(x); \ + __READ_ONCE(x); \ +}) + +#define __WRITE_ONCE(x, val) \ +do { \ + *(volatile typeof(x) *)&(x) = (val); \ +} while (0) + +#define WRITE_ONCE(x, val) \ +do { \ + compiletime_assert_rwonce_type(x); \ + __WRITE_ONCE(x, val); \ +} while (0) + +static __no_sanitize_or_inline +unsigned long __read_once_word_nocheck(const void *addr) +{ + return __READ_ONCE(*(unsigned long *)addr); +} + +/* + * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need to load a + * word from memory atomically but without telling KASAN/KCSAN. This is + * usually used by unwinding code when walking the stack of a running process. + */ +#define READ_ONCE_NOCHECK(x) \ +({ \ + compiletime_assert(sizeof(x) == sizeof(unsigned long), \ + "Unsupported access size for READ_ONCE_NOCHECK()."); \ + (typeof(x))__read_once_word_nocheck(&(x)); \ +}) + +static __no_sanitize_or_inline +unsigned long read_word_at_a_time(const void *addr) +{ + /* open-coded instrument_read(addr, 1) */ + kasan_check_read(addr, 1); + kcsan_check_read(addr, 1); + + /* + * This load can race with concurrent stores to out-of-bounds memory, + * but READ_ONCE() can't be used because it requires higher alignment + * than plain loads in arm64 builds with LTO. + */ + return *(unsigned long *)addr; +} + +#endif /* __ASSEMBLY__ */ +#endif /* __ASM_GENERIC_RWONCE_H */ -- cgit v1.3.1