From: Andy Lutomirski luto@kernel.org
commit 8891adc61dce2a8a41fc0c23262b681c3ec4b73a upstream.
The existing code accepted process_vm_readv() success or failure as long as it didn't return garbage. This is too weak: if the vsyscall page is readable, then process_vm_readv() should succeed and, if the page is not readable, then it should fail.
Signed-off-by: Andy Lutomirski luto@kernel.org Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Cc: x86@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Andy Lutomirski luto@kernel.org Cc: Jann Horn jannh@google.com Cc: John Hubbard jhubbard@nvidia.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- tools/testing/selftests/x86/test_vsyscall.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-)
--- a/tools/testing/selftests/x86/test_vsyscall.c +++ b/tools/testing/selftests/x86/test_vsyscall.c @@ -462,6 +462,17 @@ static int test_vsys_x(void) return 0; }
+/* + * Debuggers expect ptrace() to be able to peek at the vsyscall page. + * Use process_vm_readv() as a proxy for ptrace() to test this. We + * want it to work in the vsyscall=emulate case and to fail in the + * vsyscall=xonly case. + * + * It's worth noting that this ABI is a bit nutty. write(2) can't + * read from the vsyscall page on any kernel version or mode. The + * fact that ptrace() ever worked was a nice courtesy of old kernels, + * but the code to support it is fairly gross. + */ static int test_process_vm_readv(void) { #ifdef __x86_64__ @@ -477,8 +488,12 @@ static int test_process_vm_readv(void) remote.iov_len = 4096; ret = process_vm_readv(getpid(), &local, 1, &remote, 1, 0); if (ret != 4096) { - printf("[OK]\tprocess_vm_readv() failed (ret = %d, errno = %d)\n", ret, errno); - return 0; + /* + * We expect process_vm_readv() to work if and only if the + * vsyscall page is readable. + */ + printf("[%s]\tprocess_vm_readv() failed (ret = %d, errno = %d)\n", vsyscall_map_r ? "FAIL" : "OK", ret, errno); + return vsyscall_map_r ? 1 : 0; }
if (vsyscall_map_r) { @@ -488,6 +503,9 @@ static int test_process_vm_readv(void) printf("[FAIL]\tIt worked but returned incorrect data\n"); return 1; } + } else { + printf("[FAIL]\tprocess_rm_readv() succeeded, but it should have failed in this configuration\n"); + return 1; } #endif