Re: [PATCH v4 3.0-rc2-tip 2/22] 2: uprobes: Breakground page replacement.

Peter Zijlstra
2011-06-09T23:00:12Z

On Tue, 2011-06-07 at 18:28 +0530, Srikar Dronamraju wrote:
> + vaddr_old = kmap_atomic(old_page, KM_USER0);
> + vaddr_new = kmap_atomic(new_page, KM_USER1);
> +
> + memcpy(vaddr_new, vaddr_old, PAGE_SIZE);
> + /* poke the new insn in, ASSUMES we don't cross page boundary */
> + addr = vaddr;
> + vaddr &= ~PAGE_MASK;
> + memcpy(vaddr_new + vaddr, &opcode, uprobe_opcode_sz);
> +
> + kunmap_atomic(vaddr_new);
> + kunmap_atomic(vaddr_old);

> + vaddr_new = kmap_atomic(page, KM_USER0);
> + vaddr &= ~PAGE_MASK;
> + memcpy(opcode, vaddr_new + vaddr, uprobe_opcode_sz);
> + kunmap_atomic(vaddr_new);
>

Both sequences in resp {write,read}_opcode() assume the opcode doesn't
cross page boundaries but don't in fact have any assertions validating
this assumption.