On Thu, Aug 18, 2022 at 6:38 PM Linus Torvalds torvalds@linuxfoundation.org wrote:
On Thu, Aug 18, 2022 at 4:09 AM Jens Wiklander jens.wiklander@linaro.org wrote:
Fix this by adding an overflow check when calculating the end of the memory range. Also add an explicit call to access_ok() in tee_shm_register_user_buf() to catch an invalid user space address early.
I applied the access_ok() part of this which was clearly missing.
The check_add_overflow() should be pointless with that.
And the "roundup() overflows" check should just check for a zero result - if it is actually needed. Which I don't think it is on any relevant platform (the TEE subsystem only works on arm and x86).
I do think it might be worth discussing whether ALTERNATE_USER_ADDRESS_SPACE (and no-MMU) architectures should still have access_ok() check that it doesn't actually wrap around in the address space, so I've added linux-arch here.
That's m68k, PA-RISC, S390 and sparc.
In fact, I wonder if some or all of those might want to have the TASK_SIZE limit anyway - they may have a separate user address space, but several ones have some limits even then, and probably should have access_ok() check them rather than depend on the hardware then giving page fault.
For example, sparc32 has a user address space, but defines TASK_SIZE to 0xF0000000. m68k has several different case. parisc also has an actual limit.
And s390 uses
#define TASK_SIZE_MAX (-PAGE_SIZE)which is a good value and leaves a guard page at the top.
So I think the "roundup overflows" would probably be best fixed by just admitting that every architecture in practice has a TASK_SIZE_MAX anyway, and we should just make access_ok() check it.
Thanks for the detailed clarifications. I'll remove the redundant overflow checks.
Cheers, Jens
Linus