[PATCH v4 2/2] selftests/vm/pkeys: Add a regression test for setting PKRU through ptrace

Kyle Huey
2022-08-05T23:02:12Z

From: Kyle Huey <me@kylehuey.com>

This tests PTRACE_SETREGSET with NT_X86_XSTATE modifying PKRU directly and
removing the PKRU bit from XSTATE_BV.

Signed-off-by: Kyle Huey <me@kylehuey.com>
---
tools/testing/selftests/vm/pkey-x86.h | 12 +++
tools/testing/selftests/vm/protection_keys.c | 88 +++++++++++++++++++-
2 files changed, 98 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/vm/pkey-x86.h b/tools/testing/selftests/vm/pkey-x86.h
index b078ce9c6d2a..72c14cd3ddc7 100644
--- a/tools/testing/selftests/vm/pkey-x86.h
+++ b/tools/testing/selftests/vm/pkey-x86.h
@@ -104,6 +104,18 @@ static inline int cpu_has_pkeys(void)
return 1;
}

+static inline int cpu_max_xsave_size(void)
+{
+ unsigned long XSTATE_CPUID = 0xd;
+ unsigned int eax;
+ unsigned int ebx;
+ unsigned int ecx;
+ unsigned int edx;
+
+ __cpuid_count(XSTATE_CPUID, 0, eax, ebx, ecx, edx);
+ return ecx;
+}
+
static inline u32 pkey_bit_position(int pkey)
{
return pkey * PKEY_BITS_PER_PKEY;
diff --git a/tools/testing/selftests/vm/protection_keys.c b/tools/testing/selftests/vm/protection_keys.c
index 291bc1e07842..27759d3ed9cd 100644
--- a/tools/testing/selftests/vm/protection_keys.c
+++ b/tools/testing/selftests/vm/protection_keys.c
@@ -18,12 +18,13 @@
* do a plain mprotect() to a mprotect_pkey() area and make sure the pkey sticks
*
* Compile like this:
- * gcc -o protection_keys -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
- * gcc -m32 -o protection_keys_32 -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
+ * gcc -mxsave -o protection_keys -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
+ * gcc -mxsave -m32 -o protection_keys_32 -O2 -g -std=gnu99 -pthread -Wall protection_keys.c -lrt -ldl -lm
*/
#define _GNU_SOURCE
#define __SANE_USERSPACE_TYPES__
#include <errno.h>
+#include <linux/elf.h>
#include <linux/futex.h>
#include <time.h>
#include <sys/time.h>
@@ -1550,6 +1551,86 @@ void test_implicit_mprotect_exec_only_memory(int *ptr, u16 pkey)
do_not_expect_pkey_fault("plain read on recently PROT_EXEC area");
}

+#if defined(__i386__) || defined(__x86_64__)
+void test_ptrace_modifies_pkru(int *ptr, u16 pkey)
+{
+ pid_t child;
+ int status, ret;
+ int pkey_offset = pkey_reg_xstate_offset();
+ size_t xsave_size = cpu_max_xsave_size();
+ void *xsave;
+ u32 *pkey_register;
+ u64 *xstate_bv;
+ struct iovec iov;
+
+ child = fork();
+ pkey_assert(child >= 0);
+ dprintf3("[%d] fork() ret: %d\n", getpid(), child);
+ if (!child) {
+ u32 pkey_register = read_pkey_reg();
+
+ ptrace(PTRACE_TRACEME, 0, 0, 0);
+ raise(SIGSTOP);
+
+ /*
+ * need __read_pkey_reg() version so we do not do shadow_pkey_reg
+ * checking
+ */
+ if (pkey_register == __read_pkey_reg())
+ exit(1);
+
+ raise(SIGSTOP);
+
+ exit(__read_pkey_reg());
+ }
+
+ pkey_assert(child == waitpid(child, &status, 0));
+ dprintf3("[%d] waitpid(%d) status: %x\n", getpid(), child, status);
+ pkey_assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);
+
+ xsave = (void *)malloc(xsave_size);
+ pkey_assert(xsave > 0);
+
+ iov.iov_base = xsave;
+ iov.iov_len = xsave_size;
+ ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+ pkey_assert(ret == 0);
+
+ pkey_register = (u32 *)(xsave + pkey_offset);
+ pkey_assert(*pkey_register == read_pkey_reg());
+
+ *pkey_register = !read_pkey_reg();
+
+ ret = ptrace(PTRACE_SETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+ pkey_assert(ret == 0);
+
+ ret = ptrace(PTRACE_CONT, child, 0, 0);
+ pkey_assert(ret == 0);
+
+ pkey_assert(child == waitpid(child, &status, 0));
+ dprintf3("[%d] waitpid(%d) status: %x\n", getpid(), child, status);
+ pkey_assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);
+
+ ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+ pkey_assert(ret == 0);
+
+ xstate_bv = (u64 *)(xsave + 512);
+ *xstate_bv &= ~(1 << 9);
+
+ ret = ptrace(PTRACE_SETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+ pkey_assert(ret == 0);
+
+ ret = ptrace(PTRACE_CONT, child, 0, 0);
+ pkey_assert(ret == 0);
+
+ pkey_assert(child == waitpid(child, &status, 0));
+ dprintf3("[%d] waitpid(%d) status: %x\n", getpid(), child, status);
+ pkey_assert(WIFEXITED(status));
+ pkey_assert(WEXITSTATUS(status) == 0);
+ free(xsave);
+}
+#endif
+
void test_mprotect_pkey_on_unsupported_cpu(int *ptr, u16 pkey)
{
int size = PAGE_SIZE;
@@ -1585,6 +1666,9 @@ void (*pkey_tests[])(int *ptr, u16 pkey) = {
test_pkey_syscalls_bad_args,
test_pkey_alloc_exhaust,
test_pkey_alloc_free_attach_pkey0,
+#if defined(__i386__) || defined(__x86_64__)
+ test_ptrace_modifies_pkru,
+#endif
};

void run_tests_once(void)
--
2.37.0