uprobes: fix kernel info leak via "[uprobes]" vma

commit 34820304cc2cd1804ee1f8f3504ec77813d29c8e upstream.

xol_add_vma() maps the uninitialized page allocated by __create_xol_area()
into userspace. On some architectures (x86) this memory is readable even
without VM_READ, VM_EXEC results in the same pgprot_t as VM_EXEC|VM_READ,
although this doesn't really matter, debugger can read this memory anyway.

Link: https://lore.kernel.org/all/20240929162047.GA12611@redhat.com/

Reported-by: Will Deacon <will@kernel.org>
Fixes: d4b3b63 ("uprobes/core: Allocate XOL slots for uprobes use")
Cc: stable@vger.kernel.org
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

kernel/events/uprobes.c

@@ -1499,7 +1499,7 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
 	area->xol_mapping.name = "[uprobes]";
 	area->xol_mapping.fault = NULL;
 	area->xol_mapping.pages = area->pages;
-	area->pages[0] = alloc_page(GFP_HIGHUSER);
+	area->pages[0] = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
 	if (!area->pages[0])
 		goto free_bitmap;
 	area->pages[1] = NULL;