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, linux-kernel@vger.kernel.org,
clang-built-linux@googlegroups.com
Subject: [PATCH] lkdtm: fix memory copy size for WRITE_KERN
Date: Mon, 25 Jan 2021 16:56:22 +0800 [thread overview]
Message-ID: <20210125085622.2322-1-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.
Compare the address order before doing the subtraction.
Signed-off-by: Candle Sun <candle.sun@unisoc.com>
---
drivers/misc/lkdtm/perms.c | 19 +++++++++----------
1 file changed, 9 insertions(+), 10 deletions(-)
diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index 2dede2ef658f..fbfbdf89d668 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;
@@ -110,15 +110,14 @@ void lkdtm_WRITE_RO_AFTER_INIT(void)
void lkdtm_WRITE_KERN(void)
{
- size_t size;
- volatile unsigned char *ptr;
+ unsigned long value_dow = (unsigned long)do_overwritten;
+ unsigned long value_do = (unsigned long)do_nothing;
+ size_t size = (size_t)(value_dow > value_do ?
+ value_dow - value_do : value_do - value_dow);
- size = (unsigned long)do_overwritten - (unsigned long)do_nothing;
- ptr = (unsigned char *)do_overwritten;
-
- pr_info("attempting bad %zu byte write at %px\n", size, ptr);
- memcpy((void *)ptr, (unsigned char *)do_nothing, size);
- flush_icache_range((unsigned long)ptr, (unsigned long)(ptr + size));
+ pr_info("attempting bad %zu byte write at %px\n", size, do_overwritten);
+ memcpy((void *)value_dow, (void *)value_do, size);
+ flush_icache_range(value_dow, value_dow + (unsigned long)size);
pr_err("FAIL: survived bad write\n");
do_overwritten();
--
2.17.0
next reply other threads:[~2021-01-25 9:51 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 8:56 Candle Sun [this message]
2021-01-25 10:37 ` [PATCH] lkdtm: fix memory copy size for WRITE_KERN David Laight
2021-01-26 14:13 ` Candle Sun
2021-01-26 18:39 ` Nick Desaulniers
2021-01-26 22:53 ` David Laight
2021-01-27 11:00 ` Candle Sun
2021-01-27 17:42 ` Nick Desaulniers
2021-01-25 21:16 ` Nick Desaulniers
2021-01-26 14:17 ` Candle Sun
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