selftests/vm/pkeys: Add a regression test for setting PKRU through ptrace

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

Signed-off-by: Kyle Huey <[email protected]>
Signed-off-by: Dave Hansen <[email protected]>
Link: https://lore.kernel.org/all/20221115230932.7126-7-khuey%40kylehuey.com

Author: khuey

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;

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 +1551,129 @@ 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)
+{
+	u32 new_pkru;
+	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;
+
+	new_pkru = ~read_pkey_reg();
+	/* Don't make PROT_EXEC mappings inaccessible */
+	new_pkru &= ~3;
+
+	child = fork();
+	pkey_assert(child >= 0);
+	dprintf3("[%d] fork() ret: %d\n", getpid(), child);
+	if (!child) {
+		ptrace(PTRACE_TRACEME, 0, 0, 0);
+		/* Stop and allow the tracer to modify PKRU directly */
+		raise(SIGSTOP);
+
+		/*
+		 * need __read_pkey_reg() version so we do not do shadow_pkey_reg
+		 * checking
+		 */
+		if (__read_pkey_reg() != new_pkru)
+			exit(1);
+
+		/* Stop and allow the tracer to clear XSTATE_BV for PKRU */
+		raise(SIGSTOP);
+
+		if (__read_pkey_reg() != 0)
+			exit(1);
+
+		/* Stop and allow the tracer to examine PKRU */
+		raise(SIGSTOP);
+
+		exit(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);
+
+	xsave = (void *)malloc(xsave_size);
+	pkey_assert(xsave > 0);
+
+	/* Modify the PKRU register directly */
+	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 = new_pkru;
+
+	ret = ptrace(PTRACE_SETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+	pkey_assert(ret == 0);
+
+	/* Test that the modification is visible in ptrace before any execution */
+	memset(xsave, 0xCC, xsave_size);
+	ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+	pkey_assert(ret == 0);
+	pkey_assert(*pkey_register == new_pkru);
+
+	/* Execute the tracee */
+	ret = ptrace(PTRACE_CONT, child, 0, 0);
+	pkey_assert(ret == 0);
+
+	/* Test that the tracee saw the PKRU value change */
+	pkey_assert(child == waitpid(child, &status, 0));
+	dprintf3("[%d] waitpid(%d) status: %x\n", getpid(), child, status);
+	pkey_assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);
+
+	/* Test that the modification is visible in ptrace after execution */
+	memset(xsave, 0xCC, xsave_size);
+	ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+	pkey_assert(ret == 0);
+	pkey_assert(*pkey_register == new_pkru);
+
+	/* Clear the PKRU bit from XSTATE_BV */
+	xstate_bv = (u64 *)(xsave + 512);
+	*xstate_bv &= ~(1 << 9);
+
+	ret = ptrace(PTRACE_SETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+	pkey_assert(ret == 0);
+
+	/* Test that the modification is visible in ptrace before any execution */
+	memset(xsave, 0xCC, xsave_size);
+	ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+	pkey_assert(ret == 0);
+	pkey_assert(*pkey_register == 0);
+
+	ret = ptrace(PTRACE_CONT, child, 0, 0);
+	pkey_assert(ret == 0);
+
+	/* Test that the tracee saw the PKRU value go to 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);
+
+	/* Test that the modification is visible in ptrace after execution */
+	memset(xsave, 0xCC, xsave_size);
+	ret = ptrace(PTRACE_GETREGSET, child, (void *)NT_X86_XSTATE, &iov);
+	pkey_assert(ret == 0);
+	pkey_assert(*pkey_register == 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 +1709,9 @@ 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)