[LTP] [PATCH 2/2] Add madvise12 test

[Lorenzo Stoakes]

On Wed, Dec 11, 2024 at 01:30:48AM +0100, Petr Vorel wrote:
> Hi Andrea,
>
> [ I dared to Cc Lorenzo, the author of the kernel implementation ]

I'm not that scary am I? :)))

Feel free to cc- me on anything relating to this even if obviously in the
LTP project happy to be included! :)

>
> > Verify that MADV_GUARD_INSTALL is causing SIGSEGV when someone is
> > trying to access memory advised with it.
>
> Test LGTM, thanks for covering a new kernel feature.

All good, looks fine to me, though might be worth expanding over time, we
have some self tests in the kernel for this, see
tools/testing/selftests/mm/guard-pages.c.

But it's nice to have a basic LTP regression test to assert the fundamental
thing is working as it should, and also nice that you implement it from
your perspective rather than mine, where I am obviously rather influenced
by implementation details.

Also note I submitted man pages for the change, you can pull it from [0]
and view it via:

$ man --manpath=. 2 madvise

[0]:git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git

Hopefully these will get distributed around soon!

Thanks for doing this for my feature, much appreciated overall!

Cheers, Lorenzo

>
> Closes: https://github.com/linux-test-project/ltp/issues/1210
>
> > Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
> > ---
> >  runtest/syscalls                              |   1 +
> >  testcases/kernel/syscalls/madvise/.gitignore  |   1 +
> >  testcases/kernel/syscalls/madvise/madvise12.c | 102 ++++++++++++++++++++++++++
> >  3 files changed, 104 insertions(+)
>
> > diff --git a/runtest/syscalls b/runtest/syscalls
> > index 5fd62617df1a116b1d94c57ff30f74693320a2ab..ded035ee82d0e97c67cc1e7c487b010634b2d1a0 100644
> > --- a/runtest/syscalls
> > +++ b/runtest/syscalls
> > @@ -1000,6 +1000,7 @@ madvise08 madvise08
> >  madvise09 madvise09
> >  madvise10 madvise10
> >  madvise11 madvise11
> > +madvise12 madvise12
>
> >  newuname01 newuname01
>
> > diff --git a/testcases/kernel/syscalls/madvise/.gitignore b/testcases/kernel/syscalls/madvise/.gitignore
> > index 722ac3c34306bac414313f1ce36ca98d715cd04c..758e601a9c4e7682a925f16184d14f2357009bc2 100644
> > --- a/testcases/kernel/syscalls/madvise/.gitignore
> > +++ b/testcases/kernel/syscalls/madvise/.gitignore
> > @@ -8,3 +8,4 @@
> >  /madvise09
> >  /madvise10
> >  /madvise11
> > +/madvise12
> > diff --git a/testcases/kernel/syscalls/madvise/madvise12.c b/testcases/kernel/syscalls/madvise/madvise12.c
> > new file mode 100644
> > index 0000000000000000000000000000000000000000..2bdf843f016a7c9d175a31b76ae805d63c4cbc80
> > --- /dev/null
> > +++ b/testcases/kernel/syscalls/madvise/madvise12.c
> > @@ -0,0 +1,102 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * Copyright (c) 2024 Andrea Cervesato <andrea.cervesato@suse.com>
> > + */
> > +
> > +/*\
> > + * [Description]
> > + *
> > + * Verify that MADV_GUARD_INSTALL is causing SIGSEGV when someone is accessing
> > + * memory advised with it.
>
> Maybe add:
> 	* This is a test for feature implemented in
> 	* 662df3e5c376 ("mm: madvise: implement lightweight guard page mechanism")
>
> The rest LGTM.
>
> Reviewed-by: Petr Vorel <pvorel@suse.cz>
>
> Kind regards,
> Petr
>
> > + *
> > + * [Algorithm]
> > + *
> > + * - allocate a certain amount of memory
> > + * - advise memory with MADV_GUARD_INSTALL
> > + * - access to memory from within a child and verify it gets killed by SIGSEGV
> > + * - release memory with MADV_GUARD_REMOVE
> > + * - verify that memory has not been modified before child got killed
> > + * - modify memory within a new child
> > + * - verify that memory is accessable and child was not killed by SIGSEGV
> > + */
> > +
> > +#include "tst_test.h"
> > +#include "lapi/mmap.h"
> > +
> > +#define MAP_SIZE (8 * TST_KB)
> > +
> > +static char *addr;
> > +
> > +static void run(void)
> > +{
> > +	pid_t pid;
> > +	int status;
> > +
> > +	memset(addr, 0, MAP_SIZE);
> > +
> > +	TST_EXP_PASS(madvise(addr, MAP_SIZE, MADV_GUARD_INSTALL));
> > +
> > +	pid = SAFE_FORK();
> > +	if (!pid) {
> > +		tst_res(TINFO, "Modifying memory content");
> > +
> > +		memset(addr, 'a', MAP_SIZE);
> > +		exit(0);
> > +	}
> > +
> > +	SAFE_WAITPID(pid, &status, 0);
> > +
> > +	if (WIFSIGNALED(status) && WTERMSIG(status) == SIGSEGV)
> > +		tst_res(TPASS, "Child ended by SIGSEGV as expected");
> > +	else
> > +		tst_res(TFAIL, "Child: %s", tst_strstatus(status));
> > +
> > +	TST_EXP_PASS(madvise(addr, MAP_SIZE, MADV_GUARD_REMOVE));
> > +
> > +	for (int i = 0; i < MAP_SIZE; i++) {
> > +		if (addr[i] == 'a') {
> > +			tst_res(TFAIL, "Memory content has been modified");
> > +			return;
> > +		}
> > +	}
> > +
> > +	tst_res(TPASS, "Memory content didn't change");
> > +
> > +	pid = SAFE_FORK();
> > +	if (!pid) {
> > +		tst_res(TINFO, "Modifying memory content");
> > +
> > +		memset(addr, 'b', MAP_SIZE);
> > +		exit(0);
> > +	}
> > +
> > +	SAFE_WAITPID(pid, &status, 0);
> > +
> > +	if (!WIFSIGNALED(status))
> > +		tst_res(TPASS, "Child ended without being signaled");
> > +	else
> > +		tst_res(TFAIL, "Child ended with %s", tst_strstatus(status));
> > +}
> > +
> > +static void setup(void)
> > +{
> > +	addr = SAFE_MMAP(NULL, MAP_SIZE,
> > +			PROT_READ | PROT_WRITE,
> > +			MAP_PRIVATE | MAP_ANONYMOUS,
> > +			-1, 0);
> > +}
> > +
> > +static void cleanup(void)
> > +{
> > +	if (addr)
> > +		SAFE_MUNMAP(addr, MAP_SIZE);
> > +}
> > +
> > +static struct tst_test test = {
> > +	.test_all = run,
> > +	.setup = setup,
> > +	.cleanup = cleanup,
> > +	.needs_root = 1,
> > +	.forks_child = 1,
> > +	.min_kver = "6.13",
> > +};
>
> --
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