linux-kernel - Re: [RFC PATCH v6 11/12] livepatch/selftests: add data relocations test

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Date:   Wed, 16 Feb 2022 12:12:12 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kbuild@...r.kernel.org
Subject: Re: [RFC PATCH v6 11/12] livepatch/selftests: add data relocations
 test

On Wed, Feb 16, 2022 at 11:39:39AM -0500, Joe Lawrence wrote:
> 
> [ ... snip ... ]
> 
> diff --git a/lib/livepatch/test_klp_convert_data.c b/lib/livepatch/test_klp_convert_data.c
> new file mode 100644
> index 000000000000..142422664159
> --- /dev/null
> +++ b/lib/livepatch/test_klp_convert_data.c
> @@ -0,0 +1,190 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (C) 2021 Joe Lawrence <joe.lawrence@...hat.com>
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/cache.h>
> +#include <linux/livepatch.h>
> +#include "test_klp_convert.h"
> +
> +/* Small global */
> +int *p_global_small = &global_small;
> +
> +/* Small global (const) */
> +// .rela.data.rel.ro, .rela.rodata supported ???:
> +int * const p_const_global_small = &const_global_small;
> +
> +/* Small file-static */
> +static int *p_static_small = &static_small;
> +
> +/* Small file-static (constant) */
> +static int * const p_static_const_small = &static_const_small;
> +
> +/* Large global */
> +int *p_global_large[4] = {
> +	&global_large[0], &global_large[1],
> +	&global_large[2], &global_large[3],
> +};
> +
> +/* Large global (const) */
> +// .rela.data.rel.ro, .rela.rodata supported ???:
> +int * const p_const_global_large[4] = {
> +	&const_global_large[0], &const_global_large[1],
> +	&const_global_large[2], &const_global_large[3],
> +};
> +
> +/* Large file-static global */
> +static int *p_static_large[4] = {
> +	&static_large[0], &static_large[1],
> +	&static_large[2], &static_large[3],
> +};
> +
> +/* Large file-static (const) */
> +static int * const p_static_const_large[4] = {
> +	&static_const_large[0], &static_const_large[1],
> +	&static_const_large[2], &static_const_large[3],
> +};
> +
> +// .rela.data.rel.ro, .rela.rodata supported ???:
> +static int * __ro_after_init p_static_ro_after_init = &static_ro_after_init;
> +static int * __read_mostly p_static_read_mostly = &static_read_mostly;

This started getting a bit repetitive, and maybe belongs to its own set
of klp-convert unit tests (as the selftests seem closer to integration
type tests).

Anyway, I left in the .rela.<read-only> type relocations as mentioned in
the [RFC PATCH v6 03/12] livepatch: Add klp-convert tool [1].  We can
talk about whether such sections should be supported over there.

As for this test, it currently crashes ppc64le as it generates a late
klp-relocation type R_PPC64_ADDR64 in a section that was marked RO.
(IIRC such ppc64le data relocations to other .rela.<text> sections are
safe as they aren't marked RO.)

[1] https://lore.kernel.org/lkml/Yg0qgtSFNQx5Mo1i@redhat.com/

-- Joe