> On Dec 2, 2018, at 8:02 PM, Ram Pai <linuxram@xxxxxxxxxx> wrote: > >> On Thu, Nov 29, 2018 at 12:37:15PM +0100, Florian Weimer wrote: >> * Dave Hansen: >> >>>> On 11/27/18 3:57 AM, Florian Weimer wrote: >>>> I would have expected something that translates PKEY_DISABLE_WRITE | >>>> PKEY_DISABLE_READ into PKEY_DISABLE_ACCESS, and also accepts >>>> PKEY_DISABLE_ACCESS | PKEY_DISABLE_READ, for consistency with POWER. >>>> >>>> (My understanding is that PKEY_DISABLE_ACCESS does not disable all >>>> access, but produces execute-only memory.) >>> >>> Correct, it disables all data access, but not execution. >> >> So I would expect something like this (completely untested, I did not >> even compile this): > > > Ok. I re-read through the entire email thread to understand the problem and > the proposed solution. Let me summarize it below. Lets see if we are on the same > plate. > > So the problem is as follows: > > Currently the kernel supports 'disable-write' and 'disable-access'. > > On x86, cpu supports 'disable-write' and 'disable-access'. This > matches with what the kernel supports. All good. > > However on power, cpu supports 'disable-read' too. Since userspace can > program the cpu directly, userspace has the ability to set > 'disable-read' too. This can lead to inconsistency between the kernel > and the userspace. > > We want the kernel to match userspace on all architectures. > > Proposed Solution: > > Enhance the kernel to understand 'disable-read', and facilitate architectures > that understand 'disable-read' to allow it. > > Also explicitly define the semantics of disable-access as > 'disable-read and disable-write' > > Did I get this right? Assuming I did, the implementation has to do > the following -- > > On power, sys_pkey_alloc() should succeed if the init_val > is PKEY_DISABLE_READ, PKEY_DISABLE_WRITE, PKEY_DISABLE_ACCESS > or any combination of the three. > > On x86, sys_pkey_alloc() should succeed if the init_val is > PKEY_DISABLE_WRITE or PKEY_DISABLE_ACCESS or PKEY_DISABLE_READ > or any combination of the three, except PKEY_DISABLE_READ > specified all by itself. > > On all other arches, none of the flags are supported. I don’t really love having a situation where you can use different flag combinations to refer to the same mode. Also, we should document the effect these flags have on execute permission.
