Apart from read and write access, memory protection keys can
also be used for restricting execute permission of pages on
powerpc. This adds a test to verify if the feature works as
expected.
Signed-off-by: Sandipan Das <sandipan@xxxxxxxxxxxxx>
---
tools/testing/selftests/powerpc/mm/.gitignore | 1 +
tools/testing/selftests/powerpc/mm/Makefile | 3 +-
.../selftests/powerpc/mm/pkey_exec_prot.c | 388 ++++++++++++++++++
3 files changed, 391 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/powerpc/mm/pkey_exec_prot.c
diff --git a/tools/testing/selftests/powerpc/mm/.gitignore b/tools/testing/selftests/powerpc/mm/.gitignore
index 2ca523255b1b..8f841f925baa 100644
--- a/tools/testing/selftests/powerpc/mm/.gitignore
+++ b/tools/testing/selftests/powerpc/mm/.gitignore
@@ -8,3 +8,4 @@ wild_bctr
large_vm_fork_separation
bad_accesses
tlbie_test
+pkey_exec_prot
diff --git a/tools/testing/selftests/powerpc/mm/Makefile b/tools/testing/selftests/powerpc/mm/Makefile
index 2389bf791fd6..f9fa0ba7435c 100644
--- a/tools/testing/selftests/powerpc/mm/Makefile
+++ b/tools/testing/selftests/powerpc/mm/Makefile
@@ -3,7 +3,7 @@ noarg:
$(MAKE) -C ../
TEST_GEN_PROGS := hugetlb_vs_thp_test subpage_prot prot_sao segv_errors wild_bctr \
- large_vm_fork_separation bad_accesses
+ large_vm_fork_separation bad_accesses pkey_exec_prot
TEST_GEN_PROGS_EXTENDED := tlbie_test
TEST_GEN_FILES := tempfile
@@ -17,6 +17,7 @@ $(OUTPUT)/prot_sao: ../utils.c
$(OUTPUT)/wild_bctr: CFLAGS += -m64
$(OUTPUT)/large_vm_fork_separation: CFLAGS += -m64
$(OUTPUT)/bad_accesses: CFLAGS += -m64
+$(OUTPUT)/pkey_exec_prot: CFLAGS += -m64
$(OUTPUT)/tempfile:
dd if=/dev/zero of=$@ bs=64k count=1
diff --git a/tools/testing/selftests/powerpc/mm/pkey_exec_prot.c b/tools/testing/selftests/powerpc/mm/pkey_exec_prot.c
new file mode 100644
index 000000000000..7c7c93425c5e
--- /dev/null
+++ b/tools/testing/selftests/powerpc/mm/pkey_exec_prot.c
@@ -0,0 +1,388 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+/*
+ * Copyright 2020, Sandipan Das, IBM Corp.
+ *
+ * Test if applying execute protection on pages using memory
+ * protection keys works as expected.
+ */
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <signal.h>
+
+#include <unistd.h>
+#include <sys/mman.h>
+
+#include "reg.h"
+#include "utils.h"
+
+/*
+ * Older versions of libc use the Intel-specific access rights.
+ * Hence, override the definitions as they might be incorrect.
+ */
+#undef PKEY_DISABLE_ACCESS
+#define PKEY_DISABLE_ACCESS 0x3
+
+#undef PKEY_DISABLE_WRITE
+#define PKEY_DISABLE_WRITE 0x2
+
+#undef PKEY_DISABLE_EXECUTE
+#define PKEY_DISABLE_EXECUTE 0x4
+
+/* Older versions of libc do not not define this */
+#ifndef SEGV_PKUERR
+#define SEGV_PKUERR 4
+#endif
+
+#define SI_PKEY_OFFSET 0x20
+
+#define SYS_pkey_mprotect 386
+#define SYS_pkey_alloc 384
+#define SYS_pkey_free 385
+
+#define PKEY_BITS_PER_PKEY 2
+#define NR_PKEYS 32
+#define PKEY_BITS_MASK ((1UL << PKEY_BITS_PER_PKEY) - 1)
+
+#define PPC_INST_NOP 0x60000000
+#define PPC_INST_TRAP 0x7fe00008
+#define PPC_INST_BLR 0x4e800020
+
+#define sigsafe_err(msg) ({ \
+ ssize_t nbytes __attribute__((unused)); \
+ nbytes = write(STDERR_FILENO, msg, strlen(msg)); })
+
+static inline unsigned long pkeyreg_get(void)
+{
+ return mfspr(SPRN_AMR);
+}
+
+static inline void pkeyreg_set(unsigned long amr)
+{
+ set_amr(amr);
+}
+
+static void pkey_set_rights(int pkey, unsigned long rights)
+{
+ unsigned long amr, shift;
+
+ shift = (NR_PKEYS - pkey - 1) * PKEY_BITS_PER_PKEY;
+ amr = pkeyreg_get();
+ amr &= ~(PKEY_BITS_MASK << shift);
+ amr |= (rights & PKEY_BITS_MASK) << shift;
+ pkeyreg_set(amr);
+}
+
+static int sys_pkey_mprotect(void *addr, size_t len, int prot, int pkey)
+{
+ return syscall(SYS_pkey_mprotect, addr, len, prot, pkey);
+}
+
+static int sys_pkey_alloc(unsigned long flags, unsigned long rights)
+{
+ return syscall(SYS_pkey_alloc, flags, rights);
+}
+
+static int sys_pkey_free(int pkey)
+{
+ return syscall(SYS_pkey_free, pkey);
+}
+
+static volatile sig_atomic_t fault_pkey, fault_code, fault_type;
+static volatile sig_atomic_t remaining_faults;
+static volatile unsigned int *fault_addr;
+static unsigned long pgsize, numinsns;
+static unsigned int *insns;
+
+static void trap_handler(int signum, siginfo_t *sinfo, void *ctx)
+{
+ /* Check if this fault originated from the expected address */
+ if (sinfo->si_addr != (void *) fault_addr)
+ sigsafe_err("got a fault for an unexpected address\n");
+
+ _exit(1);
+}
+
+static void segv_handler(int signum, siginfo_t *sinfo, void *ctx)
+{
+ int signal_pkey;
+
+ /*
+ * In older versions of libc, siginfo_t does not have si_pkey as
+ * a member.
+ */
+#ifdef si_pkey
+ signal_pkey = sinfo->si_pkey;
+#else
+ signal_pkey = *((int *)(((char *) sinfo) + SI_PKEY_OFFSET));
+#endif
+
+ fault_code = sinfo->si_code;
+
+ /* Check if this fault originated from the expected address */
+ if (sinfo->si_addr != (void *) fault_addr) {
+ sigsafe_err("got a fault for an unexpected address\n");
+ _exit(1);
+ }
+
+ /* Check if too many faults have occurred for a single test case */
+ if (!remaining_faults) {
+ sigsafe_err("got too many faults for the same address\n");
+ _exit(1);
+ }
+
+
+ /* Restore permissions in order to continue */
+ switch (fault_code) {
+ case SEGV_ACCERR:
+ if (mprotect(insns, pgsize, PROT_READ | PROT_WRITE)) {
+ sigsafe_err("failed to set access permissions\n");
+ _exit(1);
+ }
+ break;
+ case SEGV_PKUERR:
+ if (signal_pkey != fault_pkey) {
+ sigsafe_err("got a fault for an unexpected pkey\n");
+ _exit(1);
+ }
+
+ switch (fault_type) {
+ case PKEY_DISABLE_ACCESS:
+ pkey_set_rights(fault_pkey, 0);
+ break;
+ case PKEY_DISABLE_EXECUTE:
+ /*
+ * Reassociate the exec-only pkey with the region
+ * to be able to continue. Unlike AMR, we cannot
+ * set IAMR directly from userspace to restore the
+ * permissions.
+ */
+ if (mprotect(insns, pgsize, PROT_EXEC)) {
+ sigsafe_err("failed to set execute permissions\n");
+ _exit(1);
+ }
+ break;
+ default:
+ sigsafe_err("got a fault with an unexpected type\n");
+ _exit(1);
+ }
+ break;
+ default:
+ sigsafe_err("got a fault with an unexpected code\n");
+ _exit(1);
+ }
+
+ remaining_faults--;
+}
+
+static int pkeys_unsupported(void)
+{
+ bool hash_mmu = false;
+ int pkey;
+
+ /* Protection keys are currently supported on Hash MMU only */
+ FAIL_IF(using_hash_mmu(&hash_mmu));
+ SKIP_IF(!hash_mmu);
+
+ /* Check if the system call is supported */
+ pkey = sys_pkey_alloc(0, 0);
+ SKIP_IF(pkey < 0);
+ sys_pkey_free(pkey);
+
+ return 0;
+}
+
+static int test(void)
+{
+ struct sigaction segv_act, trap_act;
+ int pkey, ret, i;
+
+ ret = pkeys_unsupported();
+ if (ret)
+ return ret;
+
+ /* Setup SIGSEGV handler */
+ segv_act.sa_handler = 0;
+ segv_act.sa_sigaction = segv_handler;
+ FAIL_IF(sigprocmask(SIG_SETMASK, 0, &segv_act.sa_mask) != 0);
+ segv_act.sa_flags = SA_SIGINFO;
+ segv_act.sa_restorer = 0;
+ FAIL_IF(sigaction(SIGSEGV, &segv_act, NULL) != 0);
+
+ /* Setup SIGTRAP handler */
+ trap_act.sa_handler = 0;
+ trap_act.sa_sigaction = trap_handler;
+ FAIL_IF(sigprocmask(SIG_SETMASK, 0, &trap_act.sa_mask) != 0);
+ trap_act.sa_flags = SA_SIGINFO;
+ trap_act.sa_restorer = 0;
+ FAIL_IF(sigaction(SIGTRAP, &trap_act, NULL) != 0);
+
+ /* Setup executable region */
+ pgsize = getpagesize();
+ numinsns = pgsize / sizeof(unsigned int);
+ insns = (unsigned int *) mmap(NULL, pgsize, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ FAIL_IF(insns == MAP_FAILED);
+
+ /* Write the instruction words */
+ for (i = 1; i < numinsns - 1; i++)
+ insns[i] = PPC_INST_NOP;
+
+ /*
+ * Set the first instruction as an unconditional trap. If
+ * the last write to this address succeeds, this should
+ * get overwritten by a no-op.
+ */
+ insns[0] = PPC_INST_TRAP;
+
+ /*
+ * Later, to jump to the executable region, we use a branch
+ * and link instruction (bctrl) which sets the return address
+ * automatically in LR. Use that to return back.
+ */
+ insns[numinsns - 1] = PPC_INST_BLR;
+
+ /* Allocate a pkey that restricts execution */
+ pkey = sys_pkey_alloc(0, PKEY_DISABLE_EXECUTE);
+ FAIL_IF(pkey < 0);
+
+ /*
+ * Pick the first instruction's address from the executable
+ * region.
+ */
+ fault_addr = insns;
+
+ /* The following two cases will avoid SEGV_PKUERR */
+ fault_type = -1;
+ fault_pkey = -1;
+
+ /*
+ * Read an instruction word from the address when AMR bits
+ * are not set i.e. the pkey permits both read and write
+ * access.
+ *
+ * This should not generate a fault as having PROT_EXEC
+ * implies PROT_READ on GNU systems. The pkey currently
+ * restricts execution only based on the IAMR bits. The
+ * AMR bits are cleared.
+ */
+ remaining_faults = 0;
+ FAIL_IF(sys_pkey_mprotect(insns, pgsize, PROT_EXEC, pkey) != 0);
+ printf("read from %p, pkey is execute-disabled, access-enabled\n",
+ (void *) fault_addr);
+ i = *fault_addr;
+ FAIL_IF(remaining_faults != 0);
+
+ /*
+ * Write an instruction word to the address when AMR bits
+ * are not set i.e. the pkey permits both read and write
+ * access.
+ *
+ * This should generate an access fault as having just
+ * PROT_EXEC also restricts writes. The pkey currently
+ * restricts execution only based on the IAMR bits. The
+ * AMR bits are cleared.
+ */
+ remaining_faults = 1;
+ FAIL_IF(sys_pkey_mprotect(insns, pgsize, PROT_EXEC, pkey) != 0);
+ printf("write to %p, pkey is execute-disabled, access-enabled\n",
+ (void *) fault_addr);
+ *fault_addr = PPC_INST_TRAP;
+ FAIL_IF(remaining_faults != 0 || fault_code != SEGV_ACCERR);
+
+ /* The following three cases will generate SEGV_PKUERR */
+ fault_type = PKEY_DISABLE_ACCESS;
+ fault_pkey = pkey;
+
+ /*
+ * Read an instruction word from the address when AMR bits
+ * are set i.e. the pkey permits neither read nor write
+ * access.
+ *
+ * This should generate a pkey fault based on AMR bits only
+ * as having PROT_EXEC implicitly allows reads.
+ */
+ remaining_faults = 1;
+ FAIL_IF(sys_pkey_mprotect(insns, pgsize, PROT_EXEC, pkey) != 0);
+ printf("read from %p, pkey is execute-disabled, access-disabled\n",
+ (void *) fault_addr);
+ pkey_set_rights(pkey, PKEY_DISABLE_ACCESS);
+ i = *fault_addr;
+ FAIL_IF(remaining_faults != 0 || fault_code != SEGV_PKUERR);
+
+ /*
+ * Write an instruction word to the address when AMR bits
+ * are set i.e. the pkey permits neither read nor write
+ * access.
+ *
+ * This should generate two faults. First, a pkey fault
+ * based on AMR bits and then an access fault since
+ * PROT_EXEC does not allow writes.
+ */
+ remaining_faults = 2;
+ FAIL_IF(sys_pkey_mprotect(insns, pgsize, PROT_EXEC, pkey) != 0);
+ printf("write to %p, pkey is execute-disabled, access-disabled\n",
+ (void *) fault_addr);
+ pkey_set_rights(pkey, PKEY_DISABLE_ACCESS);
+ *fault_addr = PPC_INST_NOP;
+ FAIL_IF(remaining_faults != 0 || fault_code != SEGV_ACCERR);
+
+ /*
+ * Jump to the executable region when AMR bits are set i.e.
+ * the pkey permits neither read nor write access.
+ *
+ * This should generate a pkey fault based on IAMR bits which
+ * are set to not permit execution. AMR bits should not affect
+ * execution.
+ *
+ * This also checks if the overwrite of the first instruction
+ * word from a trap to a no-op succeeded.
+ */
+ fault_addr = insns;
+ fault_type = PKEY_DISABLE_EXECUTE;
+ fault_pkey = pkey;
+ remaining_faults = 1;
+ FAIL_IF(sys_pkey_mprotect(insns, pgsize, PROT_EXEC, pkey) != 0);
+ pkey_set_rights(pkey, PKEY_DISABLE_ACCESS);
+ printf("execute at %p, pkey is execute-disabled, access-disabled\n",
+ (void *) fault_addr);
+ asm volatile("mtctr %0; bctrl" : : "r"(insns));
+ FAIL_IF(remaining_faults != 0 || fault_code != SEGV_PKUERR);
+
+ /*
+ * Free the current pkey and allocate a new one that is
+ * fully permissive.
+ */
+ sys_pkey_free(pkey);
+ pkey = sys_pkey_alloc(0, 0);
+
+ /*
+ * Jump to the executable region when AMR bits are not set
+ * i.e. the pkey permits read and write access.
+ *
+ * This should not generate any faults as the IAMR bits are
+ * also not set and hence will the pkey will not restrict
+ * execution.
+ */
+ fault_pkey = pkey;
+ remaining_faults = 0;
+ FAIL_IF(sys_pkey_mprotect(insns, pgsize, PROT_EXEC, pkey) != 0);
+ printf("execute at %p, pkey is execute-enabled, access-enabled\n",
+ (void *) fault_addr);
+ asm volatile("mtctr %0; bctrl" : : "r"(insns));
+ FAIL_IF(remaining_faults != 0);
+
+ /* Cleanup */
+ munmap((void *) insns, pgsize);
+ sys_pkey_free(pkey);
+
+ return 0;
+}
+
+int main(void)
+{
+ test_harness(test, "pkey_exec_prot");
+}
--
2.25.1
