selftests/powerpc: Tests for kernel accessing user memory

Introduce tests to cover simple scenarios where user is watching
memory which can be accessed by kernel as well. We also support
_MODE_EXACT with _SETHWDEBUG interface. Move those testcases outside
of _BP_RANGE condition. This will help to test _MODE_EXACT scenarios
when CONFIG_HAVE_HW_BREAKPOINT is not set, eg:

  $ ./ptrace-hwbreak
  ...
  PTRACE_SET_DEBUGREG, Kernel Access Userspace, len: 8: Ok
  PPC_PTRACE_SETHWDEBUG, MODE_EXACT, WO, len: 1: Ok
  PPC_PTRACE_SETHWDEBUG, MODE_EXACT, RO, len: 1: Ok
  PPC_PTRACE_SETHWDEBUG, MODE_EXACT, RW, len: 1: Ok
  PPC_PTRACE_SETHWDEBUG, MODE_EXACT, Kernel Access Userspace, len: 1: Ok
  success: ptrace-hwbreak

Suggested-by: Pedro Miraglia Franco de Carvalho <pedromfc@linux.ibm.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200902042945.129369-9-ravi.bangoria@linux.ibm.com

tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c

@@ -20,6 +20,8 @@
 #include <signal.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <sys/syscall.h>
+#include <linux/limits.h>
 #include "ptrace.h"
 
 #define SPRN_PVR	0x11F
@@ -44,6 +46,7 @@ struct gstruct {
 };
 static volatile struct gstruct gstruct __attribute__((aligned(512)));
 
+static volatile char cwd[PATH_MAX] __attribute__((aligned(8)));
 
 static void get_dbginfo(pid_t child_pid, struct ppc_debug_info *dbginfo)
 {
@@ -138,6 +141,9 @@ static void test_workload(void)
 			write_var(len);
 	}
 
+	/* PTRACE_SET_DEBUGREG, Kernel Access Userspace test */
+	syscall(__NR_getcwd, &cwd, PATH_MAX);
+
 	/* PPC_PTRACE_SETHWDEBUG, MODE_EXACT, WO test */
 	write_var(1);
 
@@ -150,6 +156,9 @@ static void test_workload(void)
 	else
 		read_var(1);
 
+	/* PPC_PTRACE_SETHWDEBUG, MODE_EXACT, Kernel Access Userspace test */
+	syscall(__NR_getcwd, &cwd, PATH_MAX);
+
 	/* PPC_PTRACE_SETHWDEBUG, MODE_RANGE, DW ALIGNED, WO test */
 	gstruct.a[rand() % A_LEN] = 'a';
 
@@ -293,6 +302,24 @@ static int test_set_debugreg(pid_t child_pid)
 	return 0;
 }
 
+static int test_set_debugreg_kernel_userspace(pid_t child_pid)
+{
+	unsigned long wp_addr = (unsigned long)cwd;
+	char *name = "PTRACE_SET_DEBUGREG";
+
+	/* PTRACE_SET_DEBUGREG, Kernel Access Userspace test */
+	wp_addr &= ~0x7UL;
+	wp_addr |= (1Ul << DABR_READ_SHIFT);
+	wp_addr |= (1UL << DABR_WRITE_SHIFT);
+	wp_addr |= (1UL << DABR_TRANSLATION_SHIFT);
+	ptrace_set_debugreg(child_pid, wp_addr);
+	ptrace(PTRACE_CONT, child_pid, NULL, 0);
+	check_success(child_pid, name, "Kernel Access Userspace", wp_addr, 8);
+
+	ptrace_set_debugreg(child_pid, 0);
+	return 0;
+}
+
 static void get_ppc_hw_breakpoint(struct ppc_hw_breakpoint *info, int type,
 				  unsigned long addr, int len)
 {
@@ -338,6 +365,22 @@ static void test_sethwdebug_exact(pid_t child_pid)
 	ptrace_delhwdebug(child_pid, wh);
 }
 
+static void test_sethwdebug_exact_kernel_userspace(pid_t child_pid)
+{
+	struct ppc_hw_breakpoint info;
+	unsigned long wp_addr = (unsigned long)&cwd;
+	char *name = "PPC_PTRACE_SETHWDEBUG, MODE_EXACT";
+	int len = 1; /* hardcoded in kernel */
+	int wh;
+
+	/* PPC_PTRACE_SETHWDEBUG, MODE_EXACT, Kernel Access Userspace test */
+	get_ppc_hw_breakpoint(&info, PPC_BREAKPOINT_TRIGGER_WRITE, wp_addr, 0);
+	wh = ptrace_sethwdebug(child_pid, &info);
+	ptrace(PTRACE_CONT, child_pid, NULL, 0);
+	check_success(child_pid, name, "Kernel Access Userspace", wp_addr, len);
+	ptrace_delhwdebug(child_pid, wh);
+}
+
 static void test_sethwdebug_range_aligned(pid_t child_pid)
 {
 	struct ppc_hw_breakpoint info;
@@ -452,9 +495,10 @@ static void
 run_tests(pid_t child_pid, struct ppc_debug_info *dbginfo, bool dawr)
 {
 	test_set_debugreg(child_pid);
+	test_set_debugreg_kernel_userspace(child_pid);
+	test_sethwdebug_exact(child_pid);
+	test_sethwdebug_exact_kernel_userspace(child_pid);
 	if (dbginfo->features & PPC_DEBUG_FEATURE_DATA_BP_RANGE) {
-		test_sethwdebug_exact(child_pid);
-
 		test_sethwdebug_range_aligned(child_pid);
 		if (dawr || is_8xx) {
 			test_sethwdebug_range_unaligned(child_pid);