On Tue, Jun 23, 2020 at 11:05:05AM +0200, Christoph Hellwig wrote:

On Sat, Jun 20, 2020 at 07:16:16PM -0700, Andrew Morton wrote:

quoted

On Thu, 18 Jun 2020 08:43:06 +0200 Christoph Hellwig [off-list ref] wrote:

quoted

Use PAGE_KERNEL_ROX directly instead of allocating RWX and setting the
page read-only just after the allocation.

--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c

@@ -120,15 +120,9 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 
 void *alloc_insn_page(void)
 {
-	void *page;
-
-	page = vmalloc_exec(PAGE_SIZE);
-	if (page) {
-		set_memory_ro((unsigned long)page, 1);
-		set_vm_flush_reset_perms(page);
-	}
-
-	return page;
+	return __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START, VMALLOC_END,
+			GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS,
+			NUMA_NO_NODE, __func__);
 }
 
 /* arm kprobe: install breakpoint in text */

But why.  I think this is just a cleanup, doesn't address any runtime issue?

It doesn't "fix" an issue - it just simplifies and speeds up the code.

Ok, but I don't understand the PLT comment from Peter in
20200618092754.GF576905@hirez.programming.kicks-ass.net:

  | I think this has the exact same range issue as the x86 user. But it
  | might be less fatal if their PLT magic can cover the full range.

Peter, please could you elaborate on your concern? I feel like I'm missing
some context.

Cheers,

Will