Messages in this thread Patch in this message | | | Date | Fri, 19 Nov 2021 13:44:32 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH] arm64: uaccess: fix put_user() with TTBR0 PAN |
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On Fri, Nov 19, 2021 at 11:33:06AM +0000, Will Deacon wrote: > On Thu, Nov 18, 2021 at 05:34:17PM +0100, Vincent Whitchurch wrote: > > The value argument to put_user() must be evaluated before the TTBR0 > > switch is done. Otherwise, if it is a function and the function sleeps, > > the reserved TTBR0 will be restored when the process is switched in > > again and the process will end up in an infinite loop of faults. > > > > This problem was seen with the put_user() in schedule_tail(). A similar > > fix was done for RISC-V in commit 285a76bb2cf51b0c74c634 ("riscv: > > evaluate put_user() arg before enabling user access"). > > > > Fixes: f253d827f33cb5a5990 ("arm64: uaccess: refactor __{get,put}_user") > > Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com> > > --- > > arch/arm64/include/asm/uaccess.h | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h > > index 6e2e0b7031ab..96b26fa9d3d0 100644 > > --- a/arch/arm64/include/asm/uaccess.h > > +++ b/arch/arm64/include/asm/uaccess.h > > @@ -362,10 +362,11 @@ do { \ > > #define __put_user_error(x, ptr, err) \ > > do { \ > > __typeof__(*(ptr)) __user *__p = (ptr); \ > > + __typeof__(*(__p)) __val = (x); \ > > might_fault(); \ > > if (access_ok(__p, sizeof(*__p))) { \ > > __p = uaccess_mask_ptr(__p); \ > > - __raw_put_user((x), __p, (err)); \ > > + __raw_put_user(__val, __p, (err)); \ > > } else { \ > > (err) = -EFAULT; \ > > } \ > > > Oh, nice spot! I hope you didn't lose too much time debugging if you > actually ran into this... > > Although it seems a lot less likely to cause a problem, should we do > something similar for __get_user_error() and assign to (x) outside of > the uaccess-disabled section?
I agree we should follow up with a more general cleanup to avoid any macro evaluation within user-access or tco critical sections. Since that's especially subtle for the get_*() helpers (and I beleive there may be some other latent issues in that area), I reckon we should do that as a follow-up, and shouldn't block this patch on that being done.
I'll go audit that and see what I spot.
Thanks, Mark.
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