On Tue, Mar 26, 2024 at 03:32:09PM +0100, David Hildenbrand wrote: > Let's add a simple reproducer for a scenario where GUP-fast could succeed > on secretmem folios, making vmsplice() succeed instead of failing. The > reproducer is based on a reproducer [1] by Miklos Szeredi. > > We want to perform two tests: vmsplice() when a fresh page was just > faulted in, and vmsplice() on an existing page after munmap() that > would drain certain LRU caches/batches in the kernel. > > In an ideal world, we could use fallocate(FALLOC_FL_PUNCH_HOLE) / > MADV_REMOVE to remove any existing page. As that is currently not > possible, run the test before any other tests that would allocate memory > in the secretmem fd. > > Perform the ftruncate() only once, and check the return value. > > [1] https://lkml.kernel.org/r/CAJfpegt3UCsMmxd0taOY11Uaw5U=eS1fE5dn0wZX3HF0oy8-oQ@xxxxxxxxxxxxxx > > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> > --- > tools/testing/selftests/mm/memfd_secret.c | 51 ++++++++++++++++++++++- > 1 file changed, 49 insertions(+), 2 deletions(-) > > diff --git a/tools/testing/selftests/mm/memfd_secret.c b/tools/testing/selftests/mm/memfd_secret.c > index 9b298f6a04b3..9a0597310a76 100644 > --- a/tools/testing/selftests/mm/memfd_secret.c > +++ b/tools/testing/selftests/mm/memfd_secret.c > @@ -20,6 +20,7 @@ > #include <unistd.h> > #include <errno.h> > #include <stdio.h> > +#include <fcntl.h> > > #include "../kselftest.h" > > @@ -83,6 +84,45 @@ static void test_mlock_limit(int fd) > pass("mlock limit is respected\n"); > } > > +static void test_vmsplice(int fd, const char *desc) > +{ > + ssize_t transferred; > + struct iovec iov; > + int pipefd[2]; > + char *mem; > + > + if (pipe(pipefd)) { > + fail("pipe failed: %s\n", strerror(errno)); > + return; > + } > + > + mem = mmap(NULL, page_size, prot, mode, fd, 0); > + if (mem == MAP_FAILED) { > + fail("Unable to mmap secret memory\n"); > + goto close_pipe; > + } > + > + /* > + * vmsplice() may use GUP-fast, which must also fail. Prefault the > + * page table, so GUP-fast could find it. > + */ > + memset(mem, PATTERN, page_size); > + > + iov.iov_base = mem; > + iov.iov_len = page_size; > + transferred = vmsplice(pipefd[1], &iov, 1, 0); > + > + if (transferred < 0 && errno == EFAULT) > + pass("vmsplice is blocked as expected with %s\n", desc); > + else > + fail("vmsplice: unexpected memory access with %s\n", desc); > + > + munmap(mem, page_size); > +close_pipe: > + close(pipefd[0]); > + close(pipefd[1]); > +} > + > static void try_process_vm_read(int fd, int pipefd[2]) > { > struct iovec liov, riov; > @@ -187,7 +227,6 @@ static void test_remote_access(int fd, const char *name, > return; > } > > - ftruncate(fd, page_size); > memset(mem, PATTERN, page_size); > > if (write(pipefd[1], &mem, sizeof(mem)) < 0) { > @@ -258,7 +297,7 @@ static void prepare(void) > strerror(errno)); > } > > -#define NUM_TESTS 4 > +#define NUM_TESTS 6 > > int main(int argc, char *argv[]) > { > @@ -277,9 +316,17 @@ int main(int argc, char *argv[]) > ksft_exit_fail_msg("memfd_secret failed: %s\n", > strerror(errno)); > } > + if (ftruncate(fd, page_size)) > + ksft_exit_fail_msg("ftruncate failed: %s\n", strerror(errno)); > > test_mlock_limit(fd); > test_file_apis(fd); > + /* > + * We have to run the first vmsplice test before any secretmem page was > + * allocated for this fd. > + */ > + test_vmsplice(fd, "fresh page"); > + test_vmsplice(fd, "existing page"); > test_process_vm_read(fd); > test_ptrace(fd); > > -- > 2.43.2 > -- Sincerely yours, Mike.
