Messages in this thread | | | Date | Thu, 16 Jun 2022 04:19:26 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCHv4 3/3] x86/tdx: Handle load_unaligned_zeropad() page-cross to a shared page |
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On Wed, Jun 15, 2022 at 04:34:48PM -0700, Dave Hansen wrote: > On 6/15/22 15:52, Kirill A. Shutemov wrote: > >> + vaddr = (unsigned long)insn_get_addr_ref(&insn, regs); > >> + if (vaddr / PAGE_SIZE != (vaddr + size) / PAGE_SIZE) > > Oops. I just realized it has off-by-one. It supposed to be: > > > > if (vaddr / PAGE_SIZE != (vaddr + size - 1) / PAGE_SIZE) > > That was bugging me. Glad you caught this. > > Wouldn't this be more obviously correct? > > if (ALIGN_DOWN(vaddr, PAGE_SIZE) != > ALIGN_DOWN(vaddr + size, PAGE_SIZE)) > ...
I don't think it fixes anything.
Consider the case when vaddr is 4092 and size is 4. This is legitimate access -- aligned and not page crosser.
The left side of the check will be evaluated to 0 and the right will be 1 which is wrong and will get us -EFAULT.
I cannot think of a helper that would fit the need.
-- Kirill A. Shutemov
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