On Mon, Feb 21, 2022 at 03:31:23PM +0100, Arnd Bergmann wrote:
On Mon, Feb 21, 2022 at 2:24 PM Thomas Bogendoerfer
<tsbogend@xxxxxxxxxxxxxxxx> wrote:
On Wed, Feb 16, 2022 at 02:13:23PM +0100, Arnd Bergmann wrote:
diff --git a/arch/mips/include/asm/uaccess.h b/arch/mips/include/asm/uaccess.h
index db9a8e002b62..d7c89dc3426c 100644
this doesn't work. For every access above maximum implemented virtual address
space of the CPU an address error will be issued, but not a TLB miss.
And address error isn't able to handle this situation.
Ah, so the __ex_table entry only catches TLB misses?
no, but there is no __ex_table handling in address error hanlder (yet).
Does this mean it also traps for kernel memory accesses, or do those
work again?
it will trap for every access.
If the addresses on mips64 are separate like on
sparc64 or s390, the entire access_ok() step could be replaced
by a fixup code in the exception handler. I suppose this depends on
CONFIG_EVA and you still need a limit check at least when EVA is
disabled.
only EVA has seperate address spaces for kernel/user.
Is there a reason to not also #define TASK_SIZE_MAX __UA_LIMIT like
for the 32bit case ?
For 32-bit, the __UA_LIMIT is a compile-time constant, so the check
ends up being trivial. On all other architectures, the same thing can
be done after the set_fs removal, so I was hoping it would work here
as well.
ic
I suspect doing the generic (size <= limit) && (addr <= (limit - size))
check on mips64 with the runtime limit ends up slightly slower
than the current code that checks a bit mask instead. If you like,
I'll update it this way, otherwise I'd need help in form of a patch
that changes the exception handling so __get_user/__put_user
also return -EFAULT for an address error.
that's what the patch does. For aligned accesses the patch should
do the right thing, but it breaks unaligned get_user/put_user.
Checking if the trapping vaddr is between end of CPU VM space and
TASK_MAX_SIZE before exception handling should do the trick. I'll
send a patch, if this works.
Thomas.
--
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea. [ RFC1925, 2.3 ]
