Messages in this thread | | | From | Florian Weimer <> | Subject | Re: [PATCH 07/12] mm: Pass the 4-bit protection key in via PROT_ bits to syscalls | Date | Fri, 04 Sep 2015 22:34:06 +0200 |
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* Dave Hansen:
> On 09/04/2015 01:13 PM, Florian Weimer wrote: > ... >>>>> >>> #define PROT_WRITE 0x2 /* page can be written */ >>>>> >>> #define PROT_EXEC 0x4 /* page can be executed */ >>>>> >>> #define PROT_SEM 0x8 /* page may be used for atomic ops */ >>>>> >>> +#define PROT_PKEY0 0x10 /* protection key value (bit 0) */ >>>>> >>> +#define PROT_PKEY1 0x20 /* protection key value (bit 1) */ >>>>> >>> +#define PROT_PKEY2 0x40 /* protection key value (bit 2) */ >>>>> >>> +#define PROT_PKEY3 0x80 /* protection key value (bit 3) */ >>>> >> >>>> >> Thats leaking deep Intelisms into asm-generic which makes me very >>>> >> uncomfortable. Whether we need to reserve some bits for "arch specific" >>>> >> is one question, what we do with them ought not to be leaking out. >>>> >> >>>> >> To start with trying to port code people will want to do >>>> >> >>>> >> #define PROT_PKEY0 0 >>>> >> #define PROT_PKEY1 0 >>> > >>> > Yeah, I feel pretty uncomfortable with it as well. I really don't >>> > expect these to live like this in asm-generic when I submit this. >>> > >>> > Powerpc and ia64 have _something_ resembling protection keys, so the >>> > concept isn't entirely x86 or Intel-specific. My hope would be that we >>> > do this in a way that other architectures can use. >> It will also be very painful to add additional bits. We went through >> this with the CPU affinity mask, and it still hurts it. Please use a >> more sensible interface from the start. :) > > Any suggestions?
It's difficult. I don't know what kind of programming model you expect. Could glibc use these bits for its own implementation? Or OpenSSL? Or is this intended for tightly integrated language run-times which have a very precise idea what kind of stuff runs within the same address space?
> Are you thinking that we want a completely separate syscall and > completely avoid using the PROT_* bits?
Yes, that would seem more future-proof.
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