selftests/powerpc: Add a test of wild bctr

This tests that a bctr (Branch to counter and link), ie. a function
call, to a wildly out-of-bounds address is handled correctly.

Some old kernel versions didn't handle it correctly, see eg:

  "powerpc/slb: Force a full SLB flush when we insert for a bad EA"
  https://lists.ozlabs.org/pipermail/linuxppc-dev/2017-April/157397.htmlSigned-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/include/reg.h

@@ -17,6 +17,7 @@
 				    : "memory")
 
 #define mb()		asm volatile("sync" : : : "memory");
+#define barrier()	asm volatile("" : : : "memory");
 
 #define SPRN_MMCR2     769
 #define SPRN_MMCRA     770

tools/testing/selftests/powerpc/mm/.gitignore

@@ -3,3 +3,4 @@ subpage_prot
 tempfile
 prot_sao
 segv_errors
+wild_bctr
\ No newline at end of file

tools/testing/selftests/powerpc/mm/Makefile

@@ -2,7 +2,7 @@
 noarg:
 	$(MAKE) -C ../
 
-TEST_GEN_PROGS := hugetlb_vs_thp_test subpage_prot prot_sao segv_errors
+TEST_GEN_PROGS := hugetlb_vs_thp_test subpage_prot prot_sao segv_errors wild_bctr
 TEST_GEN_FILES := tempfile
 
 top_srcdir = ../../../../..
@@ -12,6 +12,8 @@ $(TEST_GEN_PROGS): ../harness.c
 
 $(OUTPUT)/prot_sao: ../utils.c
 
+$(OUTPUT)/wild_bctr: CFLAGS += -m64
+
 $(OUTPUT)/tempfile:
 	dd if=/dev/zero of=$@ bs=64k count=1
 

tools/testing/selftests/powerpc/mm/wild_bctr.c

+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2018, Michael Ellerman, IBM Corp.
+ *
+ * Test that an out-of-bounds branch to counter behaves as expected.
+ */
+
+#include <setjmp.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <ucontext.h>
+#include <unistd.h>
+
+#include "utils.h"
+
+
+#define BAD_NIP	0x788c545a18000000ull
+
+static struct pt_regs signal_regs;
+static jmp_buf setjmp_env;
+
+static void save_regs(ucontext_t *ctxt)
+{
+	struct pt_regs *regs = ctxt->uc_mcontext.regs;
+
+	memcpy(&signal_regs, regs, sizeof(signal_regs));
+}
+
+static void segv_handler(int signum, siginfo_t *info, void *ctxt_v)
+{
+	save_regs(ctxt_v);
+	longjmp(setjmp_env, 1);
+}
+
+static void usr2_handler(int signum, siginfo_t *info, void *ctxt_v)
+{
+	save_regs(ctxt_v);
+}
+
+static int ok(void)
+{
+	printf("Everything is OK in here.\n");
+	return 0;
+}
+
+#define REG_POISON	0x5a5aUL
+#define POISONED_REG(n)	((REG_POISON << 48) | ((n) << 32) | (REG_POISON << 16) | (n))
+
+static inline void poison_regs(void)
+{
+	#define POISON_REG(n)	\
+	  "lis  " __stringify(n) "," __stringify(REG_POISON) ";" \
+	  "addi " __stringify(n) "," __stringify(n) "," __stringify(n) ";" \
+	  "sldi " __stringify(n) "," __stringify(n) ", 32 ;" \
+	  "oris " __stringify(n) "," __stringify(n) "," __stringify(REG_POISON) ";" \
+	  "addi " __stringify(n) "," __stringify(n) "," __stringify(n) ";"
+
+	asm (POISON_REG(15)
+	     POISON_REG(16)
+	     POISON_REG(17)
+	     POISON_REG(18)
+	     POISON_REG(19)
+	     POISON_REG(20)
+	     POISON_REG(21)
+	     POISON_REG(22)
+	     POISON_REG(23)
+	     POISON_REG(24)
+	     POISON_REG(25)
+	     POISON_REG(26)
+	     POISON_REG(27)
+	     POISON_REG(28)
+	     POISON_REG(29)
+	     : // inputs
+	     : // outputs
+	     : "15", "16", "17", "18", "19", "20", "21", "22", "23", "24", "25",
+	       "26", "27", "28", "29"
+	);
+	#undef POISON_REG
+}
+
+static int check_regs(void)
+{
+	unsigned long i;
+
+	for (i = 15; i <= 29; i++)
+		FAIL_IF(signal_regs.gpr[i] != POISONED_REG(i));
+
+	printf("Regs OK\n");
+	return 0;
+}
+
+static void dump_regs(void)
+{
+	for (int i = 0; i < 32; i += 4) {
+		printf("r%02d 0x%016lx  r%02d 0x%016lx  " \
+		       "r%02d 0x%016lx  r%02d 0x%016lx\n",
+		       i, signal_regs.gpr[i],
+		       i+1, signal_regs.gpr[i+1],
+		       i+2, signal_regs.gpr[i+2],
+		       i+3, signal_regs.gpr[i+3]);
+	}
+}
+
+int test_wild_bctr(void)
+{
+	int (*func_ptr)(void);
+	struct sigaction segv = {
+		.sa_sigaction = segv_handler,
+		.sa_flags = SA_SIGINFO
+	};
+	struct sigaction usr2 = {
+		.sa_sigaction = usr2_handler,
+		.sa_flags = SA_SIGINFO
+	};
+
+	FAIL_IF(sigaction(SIGSEGV, &segv, NULL));
+	FAIL_IF(sigaction(SIGUSR2, &usr2, NULL));
+
+	bzero(&signal_regs, sizeof(signal_regs));
+
+	if (setjmp(setjmp_env) == 0) {
+		func_ptr = ok;
+		func_ptr();
+
+		kill(getpid(), SIGUSR2);
+		printf("Regs before:\n");
+		dump_regs();
+		bzero(&signal_regs, sizeof(signal_regs));
+
+		poison_regs();
+
+		func_ptr = (int (*)(void))BAD_NIP;
+		func_ptr();
+
+		FAIL_IF(1); /* we didn't segv? */
+	}
+
+	FAIL_IF(signal_regs.nip != BAD_NIP);
+
+	printf("All good - took SEGV as expected branching to 0x%llx\n", BAD_NIP);
+
+	dump_regs();
+	FAIL_IF(check_regs());
+
+	return 0;
+}
+
+int main(void)
+{
+	return test_harness(test_wild_bctr, "wild_bctr");
+}