From: Andy Lutomirski <luto@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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
