Messages in this thread | | | Date | Mon, 11 Dec 2017 14:39:45 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH PTI v2 3/6] x86/vsyscall/64: Explicitly set _PAGE_USER in the pagetable hierarchy |
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* Andy Lutomirski <luto@kernel.org> wrote:
> The kernel is very erratic as to which pagetables have _PAGE_USER > set. The vsyscall page gets lucky: it seems that all of the > relevant pagetables are among the apparently arbitrary ones that set > _PAGE_USER. Rather than relying on chance, just explicitly set > _PAGE_USER. > > This will let us clean up pagetable setup to stop setting > _PAGE_USER. The added code can also be reused by pagetable > isolation to manage the _PAGE_USER bit in the usermode tables. > > Signed-off-by: Andy Lutomirski <luto@kernel.org> > --- > arch/x86/entry/vsyscall/vsyscall_64.c | 33 ++++++++++++++++++++++++++++++++- > 1 file changed, 32 insertions(+), 1 deletion(-)
Btw., would it make sense to clean up all this confusion?
In particular a 'KERNEL' pre of post fix is ambiguous in this context I think, and the PAGE_KERNEL_ prefix is actively harmful I think and is at the root of the confusion.
So if renamed it and used this nomenclature consistently instead:
PAGE_USER_ PAGE_SYSTEM_
... and got rid of PAGE_KERNEL uses in arch/x86/, then it would be obvious at first glance what kind of mapping is established in a particular place - and it would stay so in the future as well.
( There's some interaction with generic MM code which needs the original defines like PAGE_KERNEL[_EXEC], but those generic masks could be defined as aliases, to keep this cleanup within x86 for now. )
Thanks,
Ingo
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