On Mon, Sep 02, 2024 at 08:19:33AM +0200, Christophe Leroy wrote:

Le 02/09/2024 à 07:31, Omar Sandoval a écrit :

quoted

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From: Omar Sandoval <redacted>

Hi,

I hit a case where copy_to_kernel_nofault() will fault (lol): if the
destination address is in userspace and x86 Supervisor Mode Access
Prevention is enabled. Patch 2 has the details and the fix. Patch 1
renames a helper function so that its use in patch 2 makes more sense.
If the rename is too intrusive, I can drop it.

The name of the function is "copy_to_kernel". If the destination is a user
address, it is not a copy to kernel but a copy to user and you already have
the function copy_to_user() for that. copy_to_user() properly handles SMAP.

I'm not trying to copy to user. I am (well, KDB is) trying to copy to an
arbitrary address, and I want it to return an error instead of crashing
if the address is not a valid kernel address. As far as I can tell, that
is the whole point of copy_to_kernel_nofault().

Thanks,
Omar