Commit 47a2ebb7 authored by Alexey Dobriyan's avatar Alexey Dobriyan Committed by Linus Torvalds

execve: warn if process starts with executable stack

There were few episodes of silent downgrade to an executable stack over
years:

1) linking innocent looking assembly file will silently add executable
   stack if proper linker options is not given as well:

	$ 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.

Without doubt 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
many problems.

Link: http://lkml.kernel.org/r/20191208171918.GC19716@avx2Signed-off-by: default avatarAlexey Dobriyan <adobriyan@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Will Deacon <will@kernel.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent aacee544
...@@ -761,6 +761,11 @@ int setup_arg_pages(struct linux_binprm *bprm, ...@@ -761,6 +761,11 @@ int setup_arg_pages(struct linux_binprm *bprm,
goto out_unlock; goto out_unlock;
BUG_ON(prev != vma); BUG_ON(prev != vma);
if (unlikely(vm_flags & VM_EXEC)) {
pr_warn_once("process '%pD4' started with executable stack\n",
bprm->file);
}
/* Move stack pages down in memory. */ /* Move stack pages down in memory. */
if (stack_shift) { if (stack_shift) {
ret = shift_arg_pages(vma, stack_shift); ret = shift_arg_pages(vma, stack_shift);
......
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