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Date: Tue, 17 Dec 2019 15:57:09 -0800
From: Kees Cook <keescook@...omium.org>
To: Tianlin Li <tli@...italocean.com>
Cc: kernel-hardening@...ts.openwall.com, Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/misc: have the callers of set_memory_*() check
the return value
On Tue, Dec 17, 2019 at 01:45:28PM -0600, Tianlin Li wrote:
> Right now several architectures allow their set_memory_*() family of
> functions to fail, but callers may not be checking the return values.
> If set_memory_*() returns with an error, call-site assumptions may be
> infact wrong to assume that it would either succeed or not succeed at
> all. Ideally, the failure of set_memory_*() should be passed up the
> call stack, and callers should examine the failure and deal with it.
>
> Need to fix the callers and add the __must_check attribute. They also
> may not provide any level of atomicity, in the sense that the memory
> protections may be left incomplete on failure. This issue likely has a
> few steps on effects architectures:
> 1)Have all callers of set_memory_*() helpers check the return value.
> 2)Add __must_check to all set_memory_*() helpers so that new uses do
> not ignore the return value.
> 3)Add atomicity to the calls so that the memory protections aren't left
> in a partial state.
>
> This series is part of step 1. Make sram driver check the return value of
> set_memory_*().
>
> Signed-off-by: Tianlin Li <tli@...italocean.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
> drivers/misc/sram-exec.c | 21 +++++++++++++++++----
> 1 file changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/misc/sram-exec.c b/drivers/misc/sram-exec.c
> index d054e2842a5f..cb57ac6ab4c3 100644
> --- a/drivers/misc/sram-exec.c
> +++ b/drivers/misc/sram-exec.c
> @@ -85,6 +85,7 @@ void *sram_exec_copy(struct gen_pool *pool, void *dst, void *src,
> unsigned long base;
> int pages;
> void *dst_cpy;
> + int ret;
>
> mutex_lock(&exec_pool_list_mutex);
> list_for_each_entry(p, &exec_pool_list, list) {
> @@ -104,16 +105,28 @@ void *sram_exec_copy(struct gen_pool *pool, void *dst, void *src,
>
> mutex_lock(&part->lock);
>
> - set_memory_nx((unsigned long)base, pages);
> - set_memory_rw((unsigned long)base, pages);
> + ret = set_memory_nx((unsigned long)base, pages);
> + if (ret)
> + goto error_out;
> + ret = set_memory_rw((unsigned long)base, pages);
> + if (ret)
> + goto error_out;
>
> dst_cpy = fncpy(dst, src, size);
>
> - set_memory_ro((unsigned long)base, pages);
> - set_memory_x((unsigned long)base, pages);
> + ret = set_memory_ro((unsigned long)base, pages);
> + if (ret)
> + goto error_out;
> + ret = set_memory_x((unsigned long)base, pages);
> + if (ret)
> + goto error_out;
>
> mutex_unlock(&part->lock);
>
> return dst_cpy;
> +
> +error_out:
> + mutex_unlock(&part->lock);
> + return NULL;
> }
> EXPORT_SYMBOL_GPL(sram_exec_copy);
> --
> 2.17.1
>
--
Kees Cook
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