CVE-2024-50194 arm64: probes: Fix uprobes for big-endian kernels

Medium 5.5 Published 8 Nov 2024 Updated 11 May 2026

Incorrect endianness handling in arm64 uprobes on big-endian kernels can cause instruction simulation errors, leading to potential crashes or incorrect execution.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2024-50194?

CVE-2024-50194 is a medium-severity vulnerability in Linux kernel, published on 8 Nov 2024. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

arm64: probes: Fix uprobes for big-endian kernels

The arm64 uprobes code is broken for big-endian kernels as it doesn't convert the in-memory instruction encoding (which is always little-endian) into the kernel's native endianness before analyzing and simulating instructions. This may result in a few distinct problems:

* The kernel may may erroneously reject probing an instruction which can safely be probed.

* The kernel may erroneously erroneously permit stepping an instruction out-of-line when that instruction cannot be stepped out-of-line safely.

* The kernel may erroneously simulate instruction incorrectly dur to interpretting the byte-swapped encoding.

The endianness mismatch isn't caught by the compiler or sparse because:

* The arch_uprobe::{insn,ixol} fields are encoded as arrays of u8, so the compiler and sparse have no idea these contain a little-endian 32-bit value. The core uprobes code populates these with a memcpy() which similarly does not handle endianness.

* While the uprobe_opcode_t type is an alias for __le32, both arch_uprobe_analyze_insn() and arch_uprobe_skip_sstep() cast from u8[] to the similarly-named probe_opcode_t, which is an alias for u32. Hence there is no endianness conversion warning.

Fix this by changing the arch_uprobe::{insn,ixol} fields to __le32 and adding the appropriate __le32_to_cpu() conversions prior to consuming the instruction encoding. The core uprobes copies these fields as opaque ranges of bytes, and so is unaffected by this change.

At the same time, remove MAX_UINSN_BYTES and consistently use AARCH64_INSN_SIZE for clarity.

Tested with the following:

| #include <stdio.h> | #include <stdbool.h> | | #define noinline __attribute__((noinline)) | | static noinline void *adrp_self(void) | { | void *addr; | | asm volatile( | " adrp %x0, adrp_self\n" | " add %x0, %x0, :lo12:adrp_self\n" | : "=r" (addr)); | } | | | int main(int argc, char *argv) | { | void *ptr = adrp_self(); | bool equal = (ptr == adrp_self); | | printf("adrp_self => %p\n" | "adrp_self() => %p\n" | "%s\n", | adrp_self, ptr, equal ? "EQUAL" : "NOT EQUAL"); | | return 0; | }

.... where the adrp_self() function was compiled to:

| 00000000004007e0 <adrp_self>: | 4007e0: 90000000 adrp x0, 400000 <__ehdr_start> | 4007e4: 911f8000 add x0, x0, #0x7e0 | 4007e8: d65f03c0 ret

Before this patch, the ADRP is not recognized, and is assumed to be steppable, resulting in corruption of the result:

After this patch, the ADRP is correctly recognized and simulated:

Which versions are affected by CVE-2024-50194?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2024-50194?

Apply the vendor's patch.

Is CVE-2024-50194 being exploited?

There is no known exploitation of CVE-2024-50194 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as AZL-53435, AZL-53654, BELL-CVE-2024-50194, DEBIAN-CVE-2024-50194, GHSA-8p49-gjw4-jcmp, UBUNTU-CVE-2024-50194.