Re: [PATCH] i386: clean up user_mode() use

* pageexec@xxxxxxxxxxx <pageexec@xxxxxxxxxxx> wrote:

on i386 there're two macros used for testing the userland execution
mode: user_mode() and user_mode_vm(), which is not intuitive as on
many (all?) other architectures there's only user_mode() and
architecture independent code is written with user_mode() only, and
even on i386 someone can make the wrong assumption that user_mode()
works as it does on other archs.

two cases in point:
drivers/oprofile/cpu_buffer.c:oprofile_add_sample() uses user_mode()
which can lead to incorrect results if the interrupted task was in v86
mode with a code segment fooling the user_mode() selector RPL check.
also, arch/i386/kernel/kprobes.c:kprobe_exceptions_notify() used to
use user_mode() whereas it really meant user_mode_vm(), this is in
fact incorrect until 2.6.17.

to avoid such mistakes in the future, the suggested solution is to
make user_mode() on i386 consistent with the generic expectation and
make it detect any user mode execution context, that is, it should
take the role of user_mode_vm() and a new user_mode_novm() is
introduced for the i386 specific cases where v86 mode can be excluded.
in short, the patch simply does a

user_mode_vm -> user_mode
user_mode -> user_mode_novm

substitution as appropriate.

Signed-off-by: PaX Team <pageexec@xxxxxxxxxxx>


Acked-by: Ingo Molnar <mingo@xxxxxxx>

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