From: Kees Cook <keescook@chromium.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Andrew Morton <akpm@linux-foundation.org>,
"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
Helge Deller <deller@gmx.de>, Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org,
linux-arch@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3 11/12] lkdtm: Fix execute_[user]_location()
Date: Thu, 10 Feb 2022 17:01:07 -0800 [thread overview]
Message-ID: <202202101700.985C29A@keescook> (raw)
In-Reply-To: <d4688c2af08dda706d3b6786ae5ec5a74e6171f1.1634457599.git.christophe.leroy@csgroup.eu>
On Sun, Oct 17, 2021 at 02:38:24PM +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@csgroup.eu>
This looks good. I might rename variables in the future (e.g. to avoid
the churn from adding _text) but also, that does help keep it clear. :)
Acked-by: Kees Cook <keescook@chromium.org>
-Kees
> ---
> drivers/misc/lkdtm/perms.c | 37 ++++++++++++++++++++++++++++---------
> 1 file changed, 28 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
> index 035fcca441f0..1cf24c4a79e9 100644
> --- a/drivers/misc/lkdtm/perms.c
> +++ b/drivers/misc/lkdtm/perms.c
> @@ -44,19 +44,34 @@ static noinline void do_overwritten(void)
> return;
> }
>
> +static void *setup_function_descriptor(func_desc_t *fdesc, void *dst)
> +{
> + if (!have_function_descriptors())
> + return dst;
> +
> + memcpy(fdesc, do_nothing, sizeof(*fdesc));
> + fdesc->addr = (unsigned long)dst;
> + barrier();
> +
> + return fdesc;
> +}
> +
> static noinline void execute_location(void *dst, bool write)
> {
> - void (*func)(void) = dst;
> + void (*func)(void);
> + 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);
> + pr_info("attempting bad execution at %px\n", dst);
> + func = setup_function_descriptor(&fdesc, dst);
> func();
> pr_err("FAIL: func returned\n");
> }
> @@ -66,16 +81,19 @@ static void execute_user_location(void *dst)
> int copied;
>
> /* Intentionally crossing kernel/user memory boundary. */
> - void (*func)(void) = dst;
> + void (*func)(void);
> + 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);
> + pr_info("attempting bad execution at %px\n", dst);
> + func = setup_function_descriptor(&fdesc, dst);
> func();
> pr_err("FAIL: func returned\n");
> }
> @@ -153,7 +171,8 @@ void lkdtm_EXEC_VMALLOC(void)
>
> void lkdtm_EXEC_RODATA(void)
> {
> - execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS);
> + execute_location(dereference_function_descriptor(lkdtm_rodata_do_nothing),
> + CODE_AS_IS);
> }
>
> void lkdtm_EXEC_USERSPACE(void)
> --
> 2.31.1
>
--
Kees Cook
next prev parent reply other threads:[~2022-02-11 1:01 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-17 12:38 [PATCH v3 00/12] Fix LKDTM for PPC64/IA64/PARISC Christophe Leroy
2021-10-17 12:38 ` [PATCH v3 01/12] powerpc: Move and rename func_descr_t Christophe Leroy
2021-10-18 5:58 ` Nicholas Piggin
2022-02-11 0:51 ` Kees Cook
2021-10-17 12:38 ` [PATCH v3 02/12] powerpc: Use 'struct func_desc' instead of 'struct ppc64_opd_entry' Christophe Leroy
2021-10-17 12:38 ` [PATCH v3 03/12] powerpc: Remove " Christophe Leroy
2021-10-17 12:38 ` [PATCH v3 04/12] powerpc: Prepare func_desc_t for refactorisation Christophe Leroy
2021-10-18 6:27 ` Nicholas Piggin
2021-10-18 7:08 ` Christophe Leroy
2022-02-11 0:54 ` Kees Cook
2022-02-11 7:39 ` Segher Boessenkool
2022-02-14 10:30 ` Christophe Leroy
2021-10-17 12:38 ` [PATCH v3 05/12] ia64: Rename 'ip' to 'addr' in 'struct fdesc' Christophe Leroy
2021-10-17 12:38 ` [PATCH v3 06/12] asm-generic: Define CONFIG_HAVE_FUNCTION_DESCRIPTORS Christophe Leroy
2021-10-17 12:38 ` [PATCH v3 07/12] asm-generic: Define 'func_desc_t' to commonly describe function descriptors Christophe Leroy
2021-10-18 6:29 ` Nicholas Piggin
2021-10-18 7:07 ` Christophe Leroy
2021-10-18 9:16 ` Nicholas Piggin
2021-10-17 12:38 ` [PATCH v3 08/12] asm-generic: Refactor dereference_[kernel]_function_descriptor() Christophe Leroy
2022-02-10 10:30 ` Michael Ellerman
2022-02-11 0:56 ` Kees Cook
2022-02-14 10:32 ` Christophe Leroy
2021-10-17 12:38 ` [PATCH v3 09/12] lkdtm: Force do_nothing() out of line Christophe Leroy
2021-10-17 12:38 ` [PATCH v3 10/12] lkdtm: Really write into kernel text in WRITE_KERN Christophe Leroy
2021-10-17 12:38 ` [PATCH v3 11/12] lkdtm: Fix execute_[user]_location() Christophe Leroy
2021-12-17 11:49 ` Christophe Leroy
2021-12-17 17:12 ` Helge Deller
2022-01-19 19:28 ` Christophe Leroy
2022-01-19 22:00 ` Kees Cook
2022-02-11 1:01 ` Kees Cook [this message]
2021-10-17 12:38 ` [PATCH v3 12/12] lkdtm: Add a test for function descriptors protection Christophe Leroy
2022-02-11 1:09 ` Kees Cook
2022-02-14 10:34 ` Christophe Leroy
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