On Mon, Apr 15, 2024 at 12:47:50PM +0200, Peter Zijlstra wrote:
> On Thu, Apr 11, 2024 at 07:05:25PM +0300, Mike Rapoport wrote:
>
> > To populate the cache, a writable large page is allocated from vmalloc with
> > VM_ALLOW_HUGE_VMAP, filled with invalid instructions and then remapped as
> > ROX.
>
> > +static void execmem_invalidate(void *ptr, size_t size, bool writable)
> > +{
> > + if (execmem_info->invalidate)
> > + execmem_info->invalidate(ptr, size, writable);
> > + else
> > + memset(ptr, 0, size);
> > +}
>
> +static void execmem_invalidate(void *ptr, size_t size, bool writeable)
> +{
> + /* fill memory with INT3 instructions */
> + if (writeable)
> + memset(ptr, 0xcc, size);
> + else
> + text_poke_set(ptr, 0xcc, size);
> +}
>
> Thing is, 0xcc (aka INT3_INSN_OPCODE) is not an invalid instruction.
> It raises #BP not #UD.
Do you mean that _invalidate is a poor name choice or that it's necessary
to use an instruction that raises #UD?
--
Sincerely yours,
Mike.
