Re: [RFC PATCH 08/10] uaccess: Refuse and warn on __copy_from_user_inatomic() without an mm

[sashiko-bot@kernel.org]

> __copy_from_user_inatomic() never called should_fail_usercopy(), so the
> NULL current->mm check added to uaccess_should_fail() does not cover it.
> It is used e.g. by KVM's kvm_read_guest_atomic(), by several
> architectures' perf callchain and stack trace code, and by the generic
> copy_from_user_inatomic_nontemporal().
> 
> Split the NULL mm check out of uaccess_should_fail() into
> uaccess_without_mm(), and use it in __copy_from_user_inatomic() to warn
> and refuse the copy.
> 
> Don't use uaccess_should_fail() there, as that would also start injecting
> failures into __copy_from_user_inatomic(), which some callers don't
> expect to fail in practice, e.g. __wp_page_copy_user() warns if the copy
> fails twice.
> 
> copy_from_user_nofault() already fails quietly when current->mm is NULL,
> and the generic user stack unwinding entry points (perf_callchain(),
> get_perf_callchain() and stack_trace_save_user()) only unwind the user
> stack of a user task with an mm, so neither is affected.
> 
> Signed-off-by: James Houghton <jthoughton@google.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261026215226.3713941-1-jthoughton@google.com?part=8