selftests/powerpc/ptrace: Add peek/poke of FPRs

Currently the ptrace-gpr test only tests the GET/SET(FP)REGS ptrace
APIs. But there's an alternate (older) API, called PEEK/POKEUSR.

Add some minimal testing of PEEK/POKEUSR of the FPRs. This is sufficient
to detect the bug that was fixed recently in the 32-bit ptrace FPR
handling.

Depends-on: 8e127844 ("powerpc/32: Fix overread/overwrite of thread_struct via ptrace")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220627140239.2464900-13-mpe@ellerman.id.au

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

@@ -46,22 +46,42 @@ static int child(void)
 
 int trace_gpr(pid_t child)
 {
+	__u64 tmp, fpr[32], *peeked_fprs;
 	unsigned long gpr[18];
-	__u64 tmp, fpr[32];
 
 	FAIL_IF(start_trace(child));
+
+	// Check child GPRs match what we expect using GETREGS
 	FAIL_IF(show_gpr(child, gpr));
 	FAIL_IF(validate_gpr(gpr, child_gpr_val));
-	FAIL_IF(show_fpr(child, fpr));
 
+	// Check child FPRs match what we expect using GETFPREGS
+	FAIL_IF(show_fpr(child, fpr));
 	memcpy(&tmp, &child_fpr_val, sizeof(tmp));
 	FAIL_IF(validate_fpr(fpr, tmp));
 
+	// Check child FPRs match what we expect using PEEKUSR
+	peeked_fprs = peek_fprs(child);
+	FAIL_IF(!peeked_fprs);
+	FAIL_IF(validate_fpr(peeked_fprs, tmp));
+	free(peeked_fprs);
+
+	// Write child GPRs using SETREGS
 	FAIL_IF(write_gpr(child, parent_gpr_val));
 
+	// Write child FPRs using SETFPREGS
 	memcpy(&tmp, &parent_fpr_val, sizeof(tmp));
 	FAIL_IF(write_fpr(child, tmp));
 
+	// Check child FPRs match what we just set, using PEEKUSR
+	peeked_fprs = peek_fprs(child);
+	FAIL_IF(!peeked_fprs);
+	FAIL_IF(validate_fpr(peeked_fprs, tmp));
+
+	// Write child FPRs using POKEUSR
+	FAIL_IF(poke_fprs(child, (unsigned long *)peeked_fprs));
+
+	// Child will check its FPRs match before exiting
 	FAIL_IF(stop_trace(child));
 
 	return TEST_PASS;

tools/testing/selftests/powerpc/ptrace/ptrace.h

@@ -23,6 +23,7 @@
 #include <sys/ipc.h>
 #include <sys/shm.h>
 #include <sys/user.h>
+#include <sys/syscall.h>
 #include <linux/elf.h>
 #include <linux/types.h>
 #include <linux/auxvec.h>
@@ -440,6 +441,70 @@ int show_gpr(pid_t child, unsigned long *gpr)
 	return TEST_PASS;
 }
 
+long sys_ptrace(enum __ptrace_request request, pid_t pid, unsigned long addr, unsigned long data)
+{
+	return syscall(__NR_ptrace, request, pid, (void *)addr, data);
+}
+
+// 33 because of FPSCR
+#define PT_NUM_FPRS	(33 * (sizeof(__u64) / sizeof(unsigned long)))
+
+__u64 *peek_fprs(pid_t child)
+{
+	unsigned long *fprs, *p, addr;
+	long ret;
+	int i;
+
+	fprs = malloc(sizeof(unsigned long) * PT_NUM_FPRS);
+	if (!fprs) {
+		perror("malloc() failed");
+		return NULL;
+	}
+
+	for (i = 0, p = fprs; i < PT_NUM_FPRS; i++, p++) {
+		addr = sizeof(unsigned long) * (PT_FPR0 + i);
+		ret = sys_ptrace(PTRACE_PEEKUSER, child, addr, (unsigned long)p);
+		if (ret) {
+			perror("ptrace(PTRACE_PEEKUSR) failed");
+			return NULL;
+		}
+	}
+
+	addr = sizeof(unsigned long) * (PT_FPR0 + i);
+	ret = sys_ptrace(PTRACE_PEEKUSER, child, addr, (unsigned long)&addr);
+	if (!ret) {
+		printf("ptrace(PTRACE_PEEKUSR) succeeded unexpectedly!\n");
+		return NULL;
+	}
+
+	return (__u64 *)fprs;
+}
+
+int poke_fprs(pid_t child, unsigned long *fprs)
+{
+	unsigned long *p, addr;
+	long ret;
+	int i;
+
+	for (i = 0, p = fprs; i < PT_NUM_FPRS; i++, p++) {
+		addr = sizeof(unsigned long) * (PT_FPR0 + i);
+		ret = sys_ptrace(PTRACE_POKEUSER, child, addr, *p);
+		if (ret) {
+			perror("ptrace(PTRACE_POKEUSR) failed");
+			return -1;
+		}
+	}
+
+	addr = sizeof(unsigned long) * (PT_FPR0 + i);
+	ret = sys_ptrace(PTRACE_POKEUSER, child, addr, addr);
+	if (!ret) {
+		printf("ptrace(PTRACE_POKEUSR) succeeded unexpectedly!\n");
+		return -1;
+	}
+
+	return 0;
+}
+
 int write_gpr(pid_t child, unsigned long val)
 {
 	struct pt_regs *regs;