Re: [PATCH v2 0/3] Handle delay slot for extable lookup

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


在 2024/2/4 07:41, Linus Torvalds 写道:
The thing is, the only reason for the code in
get_mmap_lock_carefully() is for kernel bugs. IOW, some kernel bug
with a wild pointer, and we do not want to deadlock on the mm
semaphore, we want to get back to the fault handler and it should
report an oops.

... and one of the "wild pointers" might in fact be the instruction
pointer, in case we've branched through a NULL function pointer or
similar. IOW, the exception *source* might be the instruction pointer

Well this is the tricky part of my assumption.
In `exception_epc()` `__isa_exception_epc()` stuff is only called if we are in delay slot. It is impossible for a invalid instruction_pointer to be considered as "in delay slot"
by hardware.

I'd agree that sounds fragile though.


So I realy think that MIPS needs to have some kind of "safe kernel
exception pointer" helper. One that is guaranteed not to fault when
evaluating the exception pointer.

Assuming the kernel itself is never built with MIPS16e instructions,
maybe that's a safe assumption thanks to the "get_isa16_mode()" check
of EPC. But all of this makes me nervous.


Jiaxun Yang

[Index of Archives]     [LKML Archive]     [Linux ARM Kernel]     [Linux ARM]     [Git]     [Yosemite News]     [Linux SCSI]     [Linux Hams]

  Powered by Linux