From: Candle Sun <candlesea@gmail.com>
To: keescook@chromium.org
Cc: arnd@arndb.de, gregkh@linuxfoundation.org,
natechancellor@gmail.com, ndesaulniers@google.com,
candle.sun@unisoc.com, David.Laight@aculab.com,
linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: [PATCH v2] lkdtm: fix memory copy size for WRITE_KERN
Date: Wed, 27 Jan 2021 19:05:10 +0800 [thread overview]
Message-ID: <20210127110510.24492-1-candlesea@gmail.com> (raw)
From: Candle Sun <candle.sun@unisoc.com>
Though do_overwritten() follows do_nothing() in source code, the final
memory address order is determined by compiler. We can't always assume
address of do_overwritten() is bigger than do_nothing(). At least the
Clang we are using places do_overwritten() before do_nothing() in the
object. This causes the copy size in lkdtm_WRITE_KERN() is *really*
big and WRITE_KERN test on ARM32 arch will fail.
Get absolute value of the address substraction for memcpy() size.
Signed-off-by: Candle Sun <candle.sun@unisoc.com>
---
Changes in v2:
- Use abs() in place of address comparison.
---
drivers/misc/lkdtm/perms.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index 2dede2ef658f..fbb7f4554054 100644
--- a/drivers/misc/lkdtm/perms.c
+++ b/drivers/misc/lkdtm/perms.c
@@ -31,13 +31,13 @@ static unsigned long ro_after_init __ro_after_init = 0x55AA5500;
* This just returns to the caller. It is designed to be copied into
* non-executable memory regions.
*/
-static void do_nothing(void)
+static noinline void do_nothing(void)
{
return;
}
/* Must immediately follow do_nothing for size calculuations to work out. */
-static void do_overwritten(void)
+static noinline void do_overwritten(void)
{
pr_info("do_overwritten wasn't overwritten!\n");
return;
@@ -113,7 +113,7 @@ void lkdtm_WRITE_KERN(void)
size_t size;
volatile unsigned char *ptr;
- size = (unsigned long)do_overwritten - (unsigned long)do_nothing;
+ size = (size_t)abs((uintptr_t)do_overwritten - (uintptr_t)do_nothing);
ptr = (unsigned char *)do_overwritten;
pr_info("attempting bad %zu byte write at %px\n", size, ptr);
--
2.17.0
next reply other threads:[~2021-01-27 11:08 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-27 11:05 Candle Sun [this message]
2021-01-27 17:40 ` [PATCH v2] lkdtm: fix memory copy size for WRITE_KERN Nick Desaulniers
2021-01-28 6:46 ` Candle Sun
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