[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <2a9988ec-c115-8fe8-4c68-82eb2fa43d6b@c-s.fr>
Date: Wed, 26 Feb 2020 08:19:19 +0100
From: Christophe Leroy <christophe.leroy@....fr>
To: Russell Currey <ruscur@...sell.cc>, linuxppc-dev@...ts.ozlabs.org
Cc: joel@....id.au, mpe@...erman.id.au, ajd@...ux.ibm.com, dja@...ens.net,
npiggin@...il.com, kernel-hardening@...ts.openwall.com,
Jordan Niethe <jniethe5@...il.com>
Subject: Re: [PATCH v4 8/8] powerpc/mm: Disable set_memory() routines when
strict RWX isn't enabled
Le 26/02/2020 à 07:24, Russell Currey a écrit :
> There are a couple of reasons that the set_memory() functions are
> problematic when STRICT_KERNEL_RWX isn't enabled:
>
> - The linear mapping is a different size and apply_to_page_range()
> may modify a giant section, breaking everything
I don't understand.
> - patch_instruction() doesn't know to work around a page being marked
> RO, and will subsequently crash
Is patch_instruction() involved at all ?
>
> The latter can be replicated by building a kernel with the set_memory()
> patches but with STRICT_KERNEL_RWX off and running ftracetest.
>
> Reported-by: Jordan Niethe <jniethe5@...il.com>
> Signed-off-by: Russell Currey <ruscur@...sell.cc>
> ---
> v4: new
>
> arch/powerpc/mm/pageattr.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/mm/pageattr.c b/arch/powerpc/mm/pageattr.c
> index ee6b5e3b7604..ff111930cf5e 100644
> --- a/arch/powerpc/mm/pageattr.c
> +++ b/arch/powerpc/mm/pageattr.c
> @@ -96,12 +96,17 @@ static int set_page_attr(pte_t *ptep, unsigned long addr, void *data)
>
> int set_memory_attr(unsigned long addr, int numpages, pgprot_t prot)
Isn't it change_memory_attr() that is a problem for you ?
> {
> - unsigned long start = ALIGN_DOWN(addr, PAGE_SIZE);
> - unsigned long sz = numpages * PAGE_SIZE;
> + unsigned long start, size;
> +
> + if (!IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
> + return 0;
Doing this you break patch 7:
mark_initmem_nx() is called regardless of CONFIG_STRICT_KERNEL_RWX
__kernel_map_pages() depends on CONFIG_DEBUG_PAGEALLOC which doesn't
depend on CONFIG_STRICT_KERNEL_RWX
>
> if (!numpages)
> return 0;
>
> - return apply_to_page_range(&init_mm, start, sz, set_page_attr,
> + start = ALIGN_DOWN(addr, PAGE_SIZE);
> + size = numpages * PAGE_SIZE;
> +
> + return apply_to_page_range(&init_mm, start, size, set_page_attr,
You don't need to move start and size calculation and change the above.
> (void *)pgprot_val(prot));
> }
>
Christophe
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
