Re: text_poke, vmap and vmalloc on x86_64

[Mathieu Desnoyers]

* Mathieu Desnoyers (mathieu.desnoyers@xxxxxxxxxx) wrote:
> Hi,
> 
> I am trying to figure out why the following code seems to work fine on
> x86_32, but the update fails to happen on x86_64. Any idea why ? From
> what I see the memcpy seems to fall in a memory area which is not the
> same as the one I test at the end of the function. It only fails for
> module addresses, which are vmalloc'd. Once I fix this, I'll be able to
> send the patchset.
> 

Ah, found it. the is_vmalloc_addr() is somewhat misleading because it
does not include the vmalloc'd memory for modules, which is in a
different address space. I wonder if it has other unknown side-effects.

I used !core_kernel_text() instead.

Mathieu

> (from my own alternative.c) :
> 
> void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
> {
>         unsigned long flags;
>         char *vaddr;
>         int nr_pages = 2;
>         struct page *pages[2];
>         int i;
> 
>         if (*((uint8_t *)addr - 1) != BREAKPOINT_INSTRUCTION) {
>                 BUG_ON(len > sizeof(long));
>                 BUG_ON((((long)addr + len - 1) & ~(sizeof(long) - 1))
>                         - ((long)addr & ~(sizeof(long) - 1)));
>         }
>         if (is_vmalloc_addr(addr)) {
>                 pages[0] = vmalloc_to_page(addr);
>                 pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
>         } else {
>                 pages[0] = virt_to_page(addr);
>                 pages[1] = virt_to_page(addr + PAGE_SIZE);
>         }
>         BUG_ON(!pages[0]);
>         if (!pages[1])
>                 nr_pages = 1;
>         vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
>         BUG_ON(!vaddr);
>         local_irq_save(flags);
>         memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
>         local_irq_restore(flags);
>         vunmap(vaddr);
>         sync_core();
>         /* Could also do a CLFLUSH here to speed up CPU recovery; but
>            that causes hangs on some VIA CPUs. */
>         for (i = 0; i < len; i++)
>                 BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
>         return addr;
> }
> 
> Mathieu
> 
> -- 
> Mathieu Desnoyers
> Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
> OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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