blob: 8533dbccf4cfa5fb2758f21684ecbf228c5cf1d1 [file] [log] [blame]
From 09292b480c30f29e07e16bfe210105a9f7b9d470 Mon Sep 17 00:00:00 2001
From: Kees Cook <>
Date: Tue, 17 Sep 2019 11:00:25 -0700
Subject: [PATCH] usercopy: Avoid HIGHMEM pfn warning
commit 314eed30ede02fa925990f535652254b5bad6b65 upstream.
When running on a system with >512MB RAM with a 32-bit kernel built with:
all execve()s will fail due to argv copying into kmap()ed pages, and on
usercopy checking the calls ultimately of virt_to_page() will be looking
for "bad" kmap (highmem) pointers due to CONFIG_DEBUG_VIRTUAL=y:
------------[ cut here ]------------
kernel BUG at ../arch/x86/mm/physaddr.c:83!
invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.3.0-rc8 #6
Hardware name: Dell Inc. Inspiron 1318/0C236D, BIOS A04 01/15/2009
EIP: __phys_addr+0xaf/0x100
Call Trace:
? __might_sleep+0x80/0xa0
? kmem_cache_alloc+0x1c7/0x370
The check is from arch/x86/mm/physaddr.c:
VIRTUAL_BUG_ON((phys_addr >> PAGE_SHIFT) > max_low_pfn);
Due to the kmap() in fs/exec.c:
kaddr = kmap(kmapped_page);
if (copy_from_user(kaddr+offset, str, bytes_to_copy)) ...
Now we can fetch the correct page to avoid the pfn check. In both cases,
hardened usercopy will need to walk the page-span checker (if enabled)
to do sanity checking.
Reported-by: Randy Dunlap <>
Tested-by: Randy Dunlap <>
Fixes: f5509cc18daa ("mm: Hardened usercopy")
Cc: Matthew Wilcox <>
Signed-off-by: Kees Cook <>
Reviewed-by: Matthew Wilcox (Oracle) <>
Signed-off-by: Paul Gortmaker <>
diff --git a/mm/usercopy.c b/mm/usercopy.c
index 98e924864554..660717a1ea5c 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -11,6 +11,7 @@
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/mm.h>
+#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
@@ -227,7 +228,12 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
if (!virt_addr_valid(ptr))
- page = virt_to_head_page(ptr);
+ /*
+ * When CONFIG_HIGHMEM=y, kmap_to_page() will give either the
+ * highmem page or fallback to virt_to_page(). The following
+ * is effectively a highmem-aware virt_to_head_page().
+ */
+ page = compound_head(kmap_to_page((void *)ptr));
if (PageSlab(page)) {
/* Check slab allocator for flags and size. */