When running on a system with >512MB RAM with a 32-bit kernel built with:
CONFIG_DEBUG_VIRTUAL=y
CONFIG_HIGHMEM=y
CONFIG_HARDENED_USERCOPY=y
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:
__check_object_size+0xaf/0x3c0
? __might_sleep+0x80/0xa0
copy_strings+0x1c2/0x370
copy_strings_kernel+0x2b/0x40
__do_execve_file+0x4ca/0x810
? kmem_cache_alloc+0x1c7/0x370
do_execve+0x1b/0x20
...
fs/exec.c:
kaddr = kmap(kmapped_page);
...
if (copy_from_user(kaddr+offset, str, bytes_to_copy)) ...
Without CONFIG_DEBUG_VIRTUAL=y, these pages are effectively ignored,
so now we do the same explicitly: detect and ignore kmap pages, instead
of tripping over the check later.
Reported-by: Randy Dunlap <[email protected]>
Fixes: f5509cc18daa ("mm: Hardened usercopy")
Cc: Matthew Wilcox <[email protected]>
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
---
Randy, I dropped your other Tested-by, since this is a different
approach. I would expect the results to be identical (i.e. my testing
shows it works), but I didn't want to assume. :)
---
include/linux/highmem.h | 7 +++++++
mm/highmem.c | 2 +-
mm/usercopy.c | 3 ++-
3 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index ea5cdbd8c2c3..c881698b8023 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -64,12 +64,19 @@ static inline void totalhigh_pages_set(long val)
void kmap_flush_unused(void);
+static inline bool is_kmap(unsigned long addr)
+{
+ return (addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP));
+}
+
struct page *kmap_to_page(void *addr);
#else /* CONFIG_HIGHMEM */
static inline unsigned int nr_free_highpages(void) { return 0; }
+static inline bool is_kmap(unsigned long addr) { return false; }
+
static inline struct page *kmap_to_page(void *addr)
{
return virt_to_page(addr);
diff --git a/mm/highmem.c b/mm/highmem.c
index 107b10f9878e..e99eca4f63fa 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -151,7 +151,7 @@ struct page *kmap_to_page(void *vaddr)
{
unsigned long addr = (unsigned long)vaddr;
- if (addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP)) {
+ if (is_kmap(addr)) {
int i = PKMAP_NR(addr);
return pte_page(pkmap_page_table[i]);
}
diff --git a/mm/usercopy.c b/mm/usercopy.c
index 98e924864554..924e634cc95d 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>
@@ -224,7 +225,7 @@ static inline void check_heap_object(const void *ptr,
unsigned long n,
{
struct page *page;
- if (!virt_addr_valid(ptr))
+ if (!virt_addr_valid(ptr) || is_kmap((unsigned long)ptr))
return;
page = virt_to_head_page(ptr);
--
2.17.1
--
Kees Cook
