From 47a2ebb7f5053387f5753b524f4920b9b829f922 Mon Sep 17 00:00:00 2001 From: Alexey Dobriyan Date: Thu, 30 Jan 2020 22:17:29 -0800 Subject: 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@avx2 Signed-off-by: Alexey Dobriyan Cc: Dan Carpenter Cc: Will Deacon Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/exec.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/fs/exec.c b/fs/exec.c index 74d88dab98dd..7f4e0a89aaa8 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -761,6 +761,11 @@ int setup_arg_pages(struct linux_binprm *bprm, goto out_unlock; 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. */ if (stack_shift) { ret = shift_arg_pages(vma, stack_shift); -- cgit v1.2.3