From: Kees Cook <keescook@chromium.org>
To: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: [PATCH] lkdtm/usercopy: Expand size of "out of frame" object
Date: Wed, 16 Feb 2022 12:17:43 -0800 [thread overview]
Message-ID: <20220216201743.2088344-1-keescook@chromium.org> (raw)
To be sufficient out of range for the usercopy test to see the lifetime
mismatch, expand the size of the "bad" buffer, which will let it be
beyond current_stack_pointer regardless of stack growth direction.
Paired with the recent addition of stack depth checking under
CONFIG_HARDENED_USERCOPY=y, this will correctly start tripping again.
Reported-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/misc/lkdtm/usercopy.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
index 9161ce7ed47a..781345ea3b07 100644
--- a/drivers/misc/lkdtm/usercopy.c
+++ b/drivers/misc/lkdtm/usercopy.c
@@ -30,12 +30,12 @@ static const unsigned char test_text[] = "This is a test.\n";
*/
static noinline unsigned char *trick_compiler(unsigned char *stack)
{
- return stack + 0;
+ return stack + unconst;
}
static noinline unsigned char *do_usercopy_stack_callee(int value)
{
- unsigned char buf[32];
+ unsigned char buf[128];
int i;
/* Exercise stack to avoid everything living in registers. */
@@ -43,7 +43,12 @@ static noinline unsigned char *do_usercopy_stack_callee(int value)
buf[i] = value & 0xff;
}
- return trick_compiler(buf);
+ /*
+ * Put the target buffer in the middle of stack allocation
+ * so that we don't step on future stack users regardless
+ * of stack growth direction.
+ */
+ return trick_compiler(&buf[(128/2)-32]);
}
static noinline void do_usercopy_stack(bool to_user, bool bad_frame)
@@ -66,6 +71,10 @@ static noinline void do_usercopy_stack(bool to_user, bool bad_frame)
bad_stack -= sizeof(unsigned long);
}
+ pr_info("stack : %px\n", (void *)current_stack_pointer);
+ pr_info("good_stack: %px-%px\n", good_stack, good_stack + sizeof(good_stack));
+ pr_info("bad_stack : %px-%px\n", bad_stack, bad_stack + sizeof(good_stack));
+
user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_ANONYMOUS | MAP_PRIVATE, 0);
--
2.30.2
next reply other threads:[~2022-02-16 20:17 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-16 20:17 Kees Cook [this message]
2022-02-16 22:06 ` [PATCH] lkdtm/usercopy: Expand size of "out of frame" object kernel test robot
2022-02-16 22:56 ` kernel test robot
2022-02-18 10:30 ` Muhammad Usama Anjum
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