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 --- arch/microblaze/lib/modsi3.S | 74 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 74 insertions(+) create mode 100644 arch/microblaze/lib/modsi3.S (limited to 'arch/microblaze/lib/modsi3.S') diff --git a/arch/microblaze/lib/modsi3.S b/arch/microblaze/lib/modsi3.S new file mode 100644 index 000000000..64154865c --- /dev/null +++ b/arch/microblaze/lib/modsi3.S @@ -0,0 +1,74 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#include + +/* +* modulo operation for 32 bit integers. +* Input : op1 in Reg r5 +* op2 in Reg r6 +* Output: op1 mod op2 in Reg r3 +*/ + + .text + .globl __modsi3 + .type __modsi3, @function + .ent __modsi3 + +__modsi3: + .frame r1, 0, r15 + + addik r1, r1, -16 + swi r28, r1, 0 + swi r29, r1, 4 + swi r30, r1, 8 + swi r31, r1, 12 + + beqi r6, div_by_zero /* div_by_zero division error */ + beqi r5, result_is_zero /* result is zero */ + bgeid r5, r5_pos + /* get the sign of the result [ depends only on the first arg] */ + add r28, r5, r0 + rsubi r5, r5, 0 /* make r5 positive */ +r5_pos: + bgei r6, r6_pos + rsubi r6, r6, 0 /* make r6 positive */ +r6_pos: + addik r3, r0, 0 /* clear mod */ + addik r30, r0, 0 /* clear div */ + addik r29, r0, 32 /* initialize the loop count */ +/* first part try to find the first '1' in the r5 */ +div1: + add r5, r5, r5 /* left shift logical r5 */ + bgeid r5, div1 + addik r29, r29, -1 +div2: + /* left shift logical r5 get the '1' into the carry */ + add r5, r5, r5 + addc r3, r3, r3 /* move that bit into the mod register */ + rsub r31, r6, r3 /* try to subtract (r30 a r6) */ + blti r31, mod_too_small + /* move the r31 to mod since the result was positive */ + or r3, r0, r31 + addik r30, r30, 1 +mod_too_small: + addik r29, r29, -1 + beqi r29, loop_end + add r30, r30, r30 /* shift in the '1' into div */ + bri div2 /* div2 */ +loop_end: + bgei r28, return_here + brid return_here + rsubi r3, r3, 0 /* negate the result */ +div_by_zero: +result_is_zero: + or r3, r0, r0 /* set result to 0 [both mod as well as div are 0] */ +return_here: +/* restore values of csrs and that of r3 and the divisor and the dividend */ + lwi r28, r1, 0 + lwi r29, r1, 4 + lwi r30, r1, 8 + lwi r31, r1, 12 + rtsd r15, 8 + addik r1, r1, 16 + +.size __modsi3, . - __modsi3 +.end __modsi3 -- cgit v1.3.1