On Tue, Nov 19, 2019 at 12:52:27AM +0300, Alexey Dobriyan wrote:
> There were few episodes of silent downgrade to an executable stack:
>
> 1) linking innocent looking assembly file
>
> $ cat f.S
> .intel_syntax noprefix
> .text
> .globl f
> f:
> ret
>
> $ cat main.c
> void f(void);
> int main(void)
> {
> f();
> return 0;
> }
>
> $ gcc main.c f.S
> $ readelf -l ./a.out
> GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000
> 0x0000000000000000 0x0000000000000000 RWE 0x10
>
> 2) converting C99 nested function into a closure
> https://nullprogram.com/blog/2019/11/15/
>
> void intsort2(int *base, size_t nmemb, _Bool invert)
> {
> int cmp(const void *a, const void *b)
> {
> int r = *(int *)a - *(int *)b;
> return invert ? -r : r;
> }
> qsort(base, nmemb, sizeof(*base), cmp);
> }
>
> will silently require stack trampolines while non-closure version will not.
>
> While without a double this behaviour is documented somewhere, add a warning
> so that developers and users can at least notice. After so many years of x86_64
> having proper executable stack support it should not cause too much problems.
>
> If the system is old or CPU is old, then there will be an early warning
> against init and/or support personnel will write that "uh-oh, our Enterprise
> Software absolutely requires executable stack" and close tickets and customers
> will nod heads and life moves on.
>
> Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> ---
>
> fs/exec.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -762,6 +762,11 @@ int setup_arg_pages(struct linux_binprm *bprm,
> goto out_unlock;
> BUG_ON(prev != vma);
>
> + if (vm_flags & VM_EXEC) {
> + pr_warn_once("process '%s'/%u started with executable stack\n",
> + current->comm, current->pid);
> + }
Given that this is triggerable by userspace, is there a concern about PID
namespaces here?
Will
