Re: [PATCH v2 12/13] lkdtm: Fix execute_[user]_location()

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 





Le 15/10/2021 à 23:31, Kees Cook a écrit :
On Thu, Oct 14, 2021 at 07:50:01AM +0200, Christophe Leroy wrote:
execute_location() and execute_user_location() intent
to copy do_nothing() text and execute it at a new location.
However, at the time being it doesn't copy do_nothing() function
but do_nothing() function descriptor which still points to the
original text. So at the end it still executes do_nothing() at
its original location allthough using a copied function descriptor.

So, fix that by really copying do_nothing() text and build a new
function descriptor by copying do_nothing() function descriptor and
updating the target address with the new location.

Also fix the displayed addresses by dereferencing do_nothing()
function descriptor.

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
  drivers/misc/lkdtm/perms.c     | 25 +++++++++++++++++++++----
  include/asm-generic/sections.h |  5 +++++
  2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index 5266dc28df6e..96b3ebfcb8ed 100644
--- a/drivers/misc/lkdtm/perms.c
+++ b/drivers/misc/lkdtm/perms.c
@@ -44,19 +44,32 @@ static noinline void do_overwritten(void)
  	return;
  }
+static void *setup_function_descriptor(func_desc_t *fdesc, void *dst)
+{
+	memcpy(fdesc, do_nothing, sizeof(*fdesc));
+	fdesc->addr = (unsigned long)dst;
+	barrier();
+
+	return fdesc;
+}

How about collapsing the "have_function_descriptors()" check into
setup_function_descriptor()?

static void *setup_function_descriptor(func_desc_t *fdesc, void *dst)
{
	if (__is_defined(HAVE_FUNCTION_DESCRIPTORS)) {
		memcpy(fdesc, do_nothing, sizeof(*fdesc));
		fdesc->addr = (unsigned long)dst;
		barrier();
		return fdesc;
	} else {
		return dst;
	}
}

Ok


+
  static noinline void execute_location(void *dst, bool write)
  {
  	void (*func)(void) = dst;
+	func_desc_t fdesc;
+	void *do_nothing_text = dereference_function_descriptor(do_nothing);
- pr_info("attempting ok execution at %px\n", do_nothing);
+	pr_info("attempting ok execution at %px\n", do_nothing_text);
  	do_nothing();
if (write == CODE_WRITE) {
-		memcpy(dst, do_nothing, EXEC_SIZE);
+		memcpy(dst, do_nothing_text, EXEC_SIZE);
  		flush_icache_range((unsigned long)dst,
  				   (unsigned long)dst + EXEC_SIZE);
  	}
  	pr_info("attempting bad execution at %px\n", func);
+	if (have_function_descriptors())
+		func = setup_function_descriptor(&fdesc, dst);
  	func();
  	pr_err("FAIL: func returned\n");
  }
@@ -67,15 +80,19 @@ static void execute_user_location(void *dst)
/* Intentionally crossing kernel/user memory boundary. */
  	void (*func)(void) = dst;
+	func_desc_t fdesc;
+	void *do_nothing_text = dereference_function_descriptor(do_nothing);
- pr_info("attempting ok execution at %px\n", do_nothing);
+	pr_info("attempting ok execution at %px\n", do_nothing_text);
  	do_nothing();
- copied = access_process_vm(current, (unsigned long)dst, do_nothing,
+	copied = access_process_vm(current, (unsigned long)dst, do_nothing_text,
  				   EXEC_SIZE, FOLL_WRITE);
  	if (copied < EXEC_SIZE)
  		return;
  	pr_info("attempting bad execution at %px\n", func);
+	if (have_function_descriptors())
+		func = setup_function_descriptor(&fdesc, dst);
  	func();
  	pr_err("FAIL: func returned\n");
  }


diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index 76163883c6ff..d225318538bd 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h
@@ -70,6 +70,11 @@ typedef struct {
  } func_desc_t;
  #endif
+static inline bool have_function_descriptors(void)
+{
+	return __is_defined(HAVE_FUNCTION_DESCRIPTORS);
+}
+
  /* random extra sections (if any).  Override
   * in asm/sections.h */
  #ifndef arch_is_kernel_text

This hunk seems like it should live in a separate patch.


Ok I move it in a previous patch.





[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [eCos]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux