| Message ID | 20231214101931.1155586-1-usama.anjum@collabora.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | selftests: secretmem: Floor the memory size to the multiple of page_size | expand |
On Thu, 14 Dec 2023 15:19:30 +0500 Muhammad Usama Anjum <usama.anjum@collabora.com> wrote: > The "locked-in-memory size" limit per process can be non-multiple of > page_size. The mmap() fails if we try to allocate locked-in-memory > with same size as the allowed limit if it isn't multiple of the > page_size because mmap() rounds off the memory size to be allocated > to next multiple of page_size. > > Fix this by flooring the length to be allocated with mmap() to the > previous multiple of the page_size. I'd like to understand how this was noticed, what the ongoing effect might be, etc. To help decide which kernel version(s) need the patch. > Fixes: 76fe17ef588a ("secretmem: test: add basic selftest for memfd_secret(2)") > Reported-by: "kernelci.org bot" <bot@kernelci.org> Which is one of the reasons we're now placing a Closes: tag after a Reported-by:.
Hi Andrew, On 12/15/23 12:40 AM, Andrew Morton wrote: > On Thu, 14 Dec 2023 15:19:30 +0500 Muhammad Usama Anjum <usama.anjum@collabora.com> wrote: > >> The "locked-in-memory size" limit per process can be non-multiple of >> page_size. The mmap() fails if we try to allocate locked-in-memory >> with same size as the allowed limit if it isn't multiple of the >> page_size because mmap() rounds off the memory size to be allocated >> to next multiple of page_size. >> >> Fix this by flooring the length to be allocated with mmap() to the >> previous multiple of the page_size. > > I'd like to understand how this was noticed, what the ongoing effect > might be, etc. To help decide which kernel version(s) need the patch. This was getting triggered on KernelCI regularly because of different ulimit settings which wasn't multiple of the page_size. Find logs here: https://linux.kernelci.org/test/plan/id/657654bd8e81e654fae13532/ The bug in was present from the time test was first added. > >> Fixes: 76fe17ef588a ("secretmem: test: add basic selftest for memfd_secret(2)") >> Reported-by: "kernelci.org bot" <bot@kernelci.org> > > Which is one of the reasons we're now placing a Closes: tag after a > Reported-by:. I was looking for email report from KernelCI. But I didn't find it. Not sure if we can do something like following: Closes: https://linux.kernelci.org/test/plan/id/657654bd8e81e654fae13532/ > >
On Thu, Dec 14, 2023 at 03:19:30PM +0500, Muhammad Usama Anjum wrote: > The "locked-in-memory size" limit per process can be non-multiple of > page_size. The mmap() fails if we try to allocate locked-in-memory > with same size as the allowed limit if it isn't multiple of the > page_size because mmap() rounds off the memory size to be allocated > to next multiple of page_size. > > Fix this by flooring the length to be allocated with mmap() to the > previous multiple of the page_size. > > Fixes: 76fe17ef588a ("secretmem: test: add basic selftest for memfd_secret(2)") > Reported-by: "kernelci.org bot" <bot@kernelci.org> > Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com> > --- > tools/testing/selftests/mm/memfd_secret.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/tools/testing/selftests/mm/memfd_secret.c b/tools/testing/selftests/mm/memfd_secret.c > index 957b9e18c729..9b298f6a04b3 100644 > --- a/tools/testing/selftests/mm/memfd_secret.c > +++ b/tools/testing/selftests/mm/memfd_secret.c > @@ -62,6 +62,9 @@ static void test_mlock_limit(int fd) > char *mem; > > len = mlock_limit_cur; > + if (len % page_size != 0) > + len = (len/page_size) * page_size; > + With mlock limit smaller than a page we get zero length here and mmap will fail with -EINVAL because of it. In this case I think we can just skip the first mmap and only check that mmaping more than mlock limit fails. > mem = mmap(NULL, len, prot, mode, fd, 0); > if (mem == MAP_FAILED) { > fail("unable to mmap secret memory\n"); > -- > 2.42.0 >
On 12/15/23 3:59 PM, Mike Rapoport wrote: > On Thu, Dec 14, 2023 at 03:19:30PM +0500, Muhammad Usama Anjum wrote: >> The "locked-in-memory size" limit per process can be non-multiple of >> page_size. The mmap() fails if we try to allocate locked-in-memory >> with same size as the allowed limit if it isn't multiple of the >> page_size because mmap() rounds off the memory size to be allocated >> to next multiple of page_size. >> >> Fix this by flooring the length to be allocated with mmap() to the >> previous multiple of the page_size. >> >> Fixes: 76fe17ef588a ("secretmem: test: add basic selftest for memfd_secret(2)") >> Reported-by: "kernelci.org bot" <bot@kernelci.org> >> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com> >> --- >> tools/testing/selftests/mm/memfd_secret.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/tools/testing/selftests/mm/memfd_secret.c b/tools/testing/selftests/mm/memfd_secret.c >> index 957b9e18c729..9b298f6a04b3 100644 >> --- a/tools/testing/selftests/mm/memfd_secret.c >> +++ b/tools/testing/selftests/mm/memfd_secret.c >> @@ -62,6 +62,9 @@ static void test_mlock_limit(int fd) >> char *mem; >> >> len = mlock_limit_cur; >> + if (len % page_size != 0) >> + len = (len/page_size) * page_size; >> + > > With mlock limit smaller than a page we get zero length here and mmap will > fail with -EINVAL because of it. This test has a initialization step in prepare() where it increases the limit to at least a page if it is less than a page. Hence we'll never get len = 0 here. > In this case I think we can just skip the first mmap and only check that > mmaping more than mlock limit fails. > >> mem = mmap(NULL, len, prot, mode, fd, 0); >> if (mem == MAP_FAILED) { >> fail("unable to mmap secret memory\n"); >> -- >> 2.42.0 >> >
diff --git a/tools/testing/selftests/mm/memfd_secret.c b/tools/testing/selftests/mm/memfd_secret.c index 957b9e18c729..9b298f6a04b3 100644 --- a/tools/testing/selftests/mm/memfd_secret.c +++ b/tools/testing/selftests/mm/memfd_secret.c @@ -62,6 +62,9 @@ static void test_mlock_limit(int fd) char *mem; len = mlock_limit_cur; + if (len % page_size != 0) + len = (len/page_size) * page_size; + mem = mmap(NULL, len, prot, mode, fd, 0); if (mem == MAP_FAILED) { fail("unable to mmap secret memory\n");
The "locked-in-memory size" limit per process can be non-multiple of page_size. The mmap() fails if we try to allocate locked-in-memory with same size as the allowed limit if it isn't multiple of the page_size because mmap() rounds off the memory size to be allocated to next multiple of page_size. Fix this by flooring the length to be allocated with mmap() to the previous multiple of the page_size. Fixes: 76fe17ef588a ("secretmem: test: add basic selftest for memfd_secret(2)") Reported-by: "kernelci.org bot" <bot@kernelci.org> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com> --- tools/testing/selftests/mm/memfd_secret.c | 3 +++ 1 file changed, 3 insertions(+)