CVE-2025-71109

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

MIPS: ftrace: Fix memory corruption when kernel is located beyond 32 bits

Since commit e424054000878 ("MIPS: Tracing: Reduce the overhead of

dynamic Function Tracer"), the macro UASM_i_LA_mostly has been used,

and this macro can generate more than 2 instructions. At the same

time, the code in ftrace assumes that no more than 2 instructions can

be generated, which is why it stores them in an int[2] array. However,

as previously noted, the macro UASM_i_LA_mostly (and now UASM_i_LA)

causes a buffer overflow when _mcount is beyond 32 bits. This leads to

corruption of the variables located in the __read_mostly section.

This corruption was observed because the variable

__cpu_primary_thread_mask was corrupted, causing a hang very early

during boot.

This fix prevents the corruption by avoiding the generation of

instructions if they could exceed 2 instructions in

length. Fortunately, insn_la_mcount is only used if the instrumented

code is located outside the kernel code section, so dynamic ftrace can

still be used, albeit in a more limited scope. This is still

preferable to corrupting memory and/or crashing the kernel.