Linux-kselftest Archive on lore.kernel.org
 help / color / Atom feed
From: Dave Martin <Dave.Martin@arm.com>
To: Cristian Marussi <cristian.marussi@arm.com>
Cc: linux-kselftest@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, shuah@kernel.org,
	amit.kachhap@arm.com, andreyknvl@google.com
Subject: Re: [PATCH v6 06/11] kselftest: arm64: fake_sigreturn_bad_magic
Date: Tue, 17 Sep 2019 17:06:03 +0100
Message-ID: <20190917160603.GN27757@arm.com> (raw)
In-Reply-To: <20190910123111.33478-7-cristian.marussi@arm.com>

On Tue, Sep 10, 2019 at 01:31:06pm +0100, Cristian Marussi wrote:
> Add a simple fake_sigreturn testcase which builds a ucontext_t with a bad
> magic header and place it onto the stack. Expects a SIGSEGV on test PASS.
> 
> Introduce a common utility assembly trampoline function to invoke a
> sigreturn while placing the provided sigframe at wanted alignment and
> also an helper to make space when needed inside the sigframe reserved
> area.
> 
> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> ---
> v5 --> v6
> - fake_sigreturn: cleaned up, avoiding excessive SP misalignments
> - fake_sigreturn: better formatting and prologue
> - get_starting_header: cleand up and commented
> - avoid timeout on failure

[...]

> diff --git a/tools/testing/selftests/arm64/signal/signals.S b/tools/testing/selftests/arm64/signal/signals.S
> new file mode 100644
> index 000000000000..e670f8f2c8de
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/signal/signals.S
> @@ -0,0 +1,64 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2019 ARM Limited */
> +
> +#include <asm/unistd.h>
> +
> +.section        .rodata, "a"
> +call_fmt:
> +	.asciz "Calling sigreturn with fake sigframe sized:%zd at SP @%08lX\n"
> +
> +.text
> +
> +.globl fake_sigreturn
> +
> +/*	fake_sigreturn	x0:&sigframe,  x1:sigframe_size,  x2:misalign_bytes */
> +fake_sigreturn:
> +	stp	x29, x30, [sp, #-16]!
> +	mov	x29, sp
> +
> +	mov	x20, x0
> +	mov	x21, x1
> +	mov	x22, x2
> +
> +	/* create space on the stack for fake sigframe 16 bytes-aligned */
> +	add	x0, x21, x22
> +	add	x0, x0, #16
> +	bic	x0, x0, #15 /* round_up(sigframe_size + misalign_bytes, 16) */

If I've figured this out right, x0 as computed here actually looks
like round_up(sigframe_size + misalign_bytes + 1, 16) - 1.

(n + (m - 1)) & ~(m - 1) is the classic way to round up when m is a
power of 2.

That's why I originally suggested to add 15.  Your code works, but I
think it always allocates at least one byte more than needed (?)

This is not a huge deal, and better than allocating one byte to few,
but it would be good to understand whether this behaviour was
intentional or not.

> +	sub	sp, sp, x0
> +	add	x23, sp, x22 /* new sigframe base with misaligment if any */
> +
> +	ldr	x0, =call_fmt
> +	mov	x1, x21
> +	mov	x2, x23
> +	bl	printf
> +
> +	/* memcpy the provided content, while still keeping SP aligned */
> +	mov	x0, x23
> +	mov	x1, x20
> +	mov	x2, x21
> +	bl	memcpy
> +
> +	/*
> +	 * Here saving a last minute SP to current->token acts as a marker:
> +	 * if we got here, we are successfully faking a sigreturn; in other
> +	 * words we are sure no bad fatal signal has been raised till now
> +	 * for unrelated reasons, so we should consider the possibly observed
> +	 * fatal signal like SEGV coming from Kernel restore_sigframe() and
> +	 * triggered as expected from our test-case.
> +	 * For simplicity this assumes that current field 'token' is laid out
> +	 * as first in struct tdescr
> +	 */
> +	ldr	x0, current
> +	str	x23, [x0]
> +	/* finally move SP to misaligned address...if any requested */
> +	mov	sp, x23
> +
> +	mov	x8, #__NR_rt_sigreturn
> +	svc	#0
> +
> +	/*
> +	 * Above sigreturn should not return...looping here leads to a timeout
> +	 * and ensure proper and clean test failure, instead of jumping around
> +	 * on a potentially corrupted stack.
> +	 */
> +	b	.

[...]

> diff --git a/tools/testing/selftests/arm64/signal/testcases/testcases.c b/tools/testing/selftests/arm64/signal/testcases/testcases.c
> index 1914a01222a1..e3521949b800 100644
> --- a/tools/testing/selftests/arm64/signal/testcases/testcases.c
> +++ b/tools/testing/selftests/arm64/signal/testcases/testcases.c
> @@ -148,3 +148,49 @@ bool validate_reserved(ucontext_t *uc, size_t resv_sz, char **err)
>  
>  	return true;
>  }
> +
> +/*
> + * This function walks through the records inside the provided reserved area
> + * trying to find enough space to fit @need_sz bytes: if not enough space is
> + * available and an extra_context record is present, it throws away the
> + * extra_context record.
> + *
> + * It returns a pointer to a new header where it is possible to start storing
> + * our need_sz bytes.
> + *
> + * @shead: points to the start of reserved area
> + * @need_sz: needed bytes
> + * @resv_sz: reserved area size in bytes
> + * @offset: if not null, this will be filled with the offset of the return
> + *	    head pointer from @shead
> + *
> + * @return: pointer to a new head where to start storing need_sz bytes, or
> + *	    NULL if space could not be made available.
> + */

That's much clearer now, thanks for that.

> +struct _aarch64_ctx *get_starting_head(struct _aarch64_ctx *shead,
> +				       size_t need_sz, size_t resv_sz,
> +				       size_t *offset)
> +{

[...]

Cheers
---Dave

  reply index

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-10 12:31 [PATCH v6 00/11] Add arm64/signal initial kselftest support Cristian Marussi
2019-09-10 12:31 ` [PATCH v6 01/11] kselftest: arm64: extend toplevel skeleton Makefile Cristian Marussi
2019-09-17 13:42   ` Anders Roxell
2019-09-17 15:17     ` Cristian Marussi
2019-09-17 15:29       ` shuah
2019-09-17 15:58         ` Cristian Marussi
2019-09-17 16:16           ` shuah
2019-09-17 16:05   ` Dave Martin
2019-09-17 16:18     ` shuah
2019-09-18 10:17       ` Dave Martin
2019-09-18 10:59       ` Cristian Marussi
2019-10-07 18:22     ` Cristian Marussi
2019-09-10 12:31 ` [PATCH v6 02/11] kselftest: arm64: mangle_pstate_invalid_compat_toggle and common utils Cristian Marussi
2019-09-17 16:05   ` Dave Martin
2019-09-26 11:00     ` Cristian Marussi
2019-09-10 12:31 ` [PATCH v6 03/11] kselftest: arm64: mangle_pstate_invalid_daif_bits Cristian Marussi
2019-09-10 12:31 ` [PATCH v6 04/11] kselftest: arm64: mangle_pstate_invalid_mode_el[123][ht] Cristian Marussi
2019-09-10 12:31 ` [PATCH v6 05/11] kselftest: arm64: mangle_pstate_ssbs_regs Cristian Marussi
2019-09-17 16:05   ` Dave Martin
2019-10-07 18:23     ` Cristian Marussi
2019-10-08 15:07       ` Dave Martin
2019-09-10 12:31 ` [PATCH v6 06/11] kselftest: arm64: fake_sigreturn_bad_magic Cristian Marussi
2019-09-17 16:06   ` Dave Martin [this message]
2019-10-07 18:23     ` Cristian Marussi
2019-09-10 12:31 ` [PATCH v6 07/11] kselftest: arm64: fake_sigreturn_bad_size_for_magic0 Cristian Marussi
2019-09-10 12:31 ` [PATCH v6 08/11] kselftest: arm64: fake_sigreturn_missing_fpsimd Cristian Marussi
2019-09-10 12:31 ` [PATCH v6 09/11] kselftest: arm64: fake_sigreturn_duplicated_fpsimd Cristian Marussi
2019-09-17 16:06   ` Dave Martin
2019-09-10 12:31 ` [PATCH v6 10/11] kselftest: arm64: fake_sigreturn_bad_size Cristian Marussi
2019-09-10 12:31 ` [PATCH v6 11/11] kselftest: arm64: fake_sigreturn_misaligned_sp Cristian Marussi

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190917160603.GN27757@arm.com \
    --to=dave.martin@arm.com \
    --cc=amit.kachhap@arm.com \
    --cc=andreyknvl@google.com \
    --cc=cristian.marussi@arm.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=shuah@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-kselftest Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-kselftest/0 linux-kselftest/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-kselftest linux-kselftest/ https://lore.kernel.org/linux-kselftest \
		linux-kselftest@vger.kernel.org
	public-inbox-index linux-kselftest

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kselftest


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git