Messages in this thread | | | Subject | Re: [PATCH v5 4/4] sparc64: Add support for ADI (Application Data Integrity) | From | Khalid Aziz <> | Date | Wed, 25 Jan 2017 15:20:33 -0700 |
| |
On 01/25/2017 03:00 PM, Rob Gardner wrote: > On 01/25/2017 12:57 PM, Khalid Aziz wrote: >> >> @@ -157,6 +158,24 @@ int __get_user_pages_fast(unsigned long start, >> int nr_pages, int write, >> pgd_t *pgdp; >> int nr = 0; >> +#ifdef CONFIG_SPARC64 >> + if (adi_capable()) { >> + long addr = start; >> + >> + /* If userspace has passed a versioned address, kernel >> + * will not find it in the VMAs since it does not store >> + * the version tags in the list of VMAs. Storing version >> + * tags in list of VMAs is impractical since they can be >> + * changed any time from userspace without dropping into >> + * kernel. Any address search in VMAs will be done with >> + * non-versioned addresses. Ensure the ADI version bits >> + * are dropped here by sign extending the last bit before >> + * ADI bits. IOMMU does not implement version tags. >> + */ >> + addr = (addr << (long)adi_nbits()) >> (long)adi_nbits(); > > > So you are depending on the sign extension to clear the ADI bits... but > this only happens if there is a zero in that "last bit before ADI bits". > If the last bit is a 1, then the ADI bits will be set instead of > cleared. That seems like an unintended consequence given the comment. I > am aware of the value of adi_nbits() and of the number of valid bits in > a virtual address on the M7 processor, but wouldn't using 'unsigned > long' for everything here guarantee the ADI bits get cleared regardless > of the state of the last non-adi bit?
Sign extension is the right thing to do. MMU considers values of 0 and 15 for bits 63-60 to be untagged addresses and expects bit 59 to be sign-extended for untagged virtual addresses. The code I added is explicitly meant to sign-extend, not zero out the top 4 bits.
-- Khalid
| |