[PATCH v2] selftests: powerpc: Add test for execute-disabled pkeys
Sandipan Das
sandipan at linux.ibm.com
Wed May 27 13:03:42 AEST 2020
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 at linux.ibm.com>
---
Previous versions can be found at
v1: https://lore.kernel.org/linuxppc-dev/20200508162332.65316-1-sandipan@linux.ibm.com/
Changes in v2:
- Added .gitignore entry for test binary.
- Fixed builds for older distros where siginfo_t might not have si_pkey as
a formal member based on discussion with Michael.
---
tools/testing/selftests/powerpc/mm/.gitignore | 1 +
tools/testing/selftests/powerpc/mm/Makefile | 3 +-
.../selftests/powerpc/mm/pkey_exec_prot.c | 336 ++++++++++++++++++
3 files changed, 339 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 b9103c4bb414..2816229f648b 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..147fb9ed47d5
--- /dev/null
+++ b/tools/testing/selftests/powerpc/mm/pkey_exec_prot.c
@@ -0,0 +1,336 @@
+// 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 <time.h>
+#include <unistd.h>
+#include <sys/mman.h>
+
+#include "utils.h"
+
+/* Override definitions as they might be inconsistent */
+#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 distros might 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)
+
+static unsigned long pkeyreg_get(void)
+{
+ unsigned long uamr;
+
+ asm volatile("mfspr %0, 0xd" : "=r"(uamr));
+ return uamr;
+}
+
+static void pkeyreg_set(unsigned long uamr)
+{
+ asm volatile("isync; mtspr 0xd, %0; isync;" : : "r"(uamr));
+}
+
+static void pkey_set_rights(int pkey, unsigned long rights)
+{
+ unsigned long uamr, shift;
+
+ shift = (NR_PKEYS - pkey - 1) * PKEY_BITS_PER_PKEY;
+ uamr = pkeyreg_get();
+ uamr &= ~(PKEY_BITS_MASK << shift);
+ uamr |= (rights & PKEY_BITS_MASK) << shift;
+ pkeyreg_set(uamr);
+}
+
+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 int fpkey, fcode, ftype, faults;
+static unsigned long pgsize, numinsns;
+static volatile unsigned int *faddr;
+static unsigned int *insns;
+
+static void segv_handler(int signum, siginfo_t *sinfo, void *ctx)
+{
+ int pkey;
+
+#ifdef si_pkey
+ pkey = sinfo->si_pkey;
+#else
+ pkey = *((int *)(((char *) sinfo) + SI_PKEY_OFFSET));
+#endif
+
+ /* Check if this fault originated because of the expected reasons */
+ if (sinfo->si_code != SEGV_ACCERR && sinfo->si_code != SEGV_PKUERR) {
+ printf("got an unexpected fault, code = %d\n",
+ sinfo->si_code);
+ goto fail;
+ }
+
+ /* Check if this fault originated from the expected address */
+ if (sinfo->si_addr != (void *) faddr) {
+ printf("got an unexpected fault, addr = %p\n",
+ sinfo->si_addr);
+ goto fail;
+ }
+
+ /* Check if the expected number of faults has been exceeded */
+ if (faults == 0)
+ goto fail;
+
+ fcode = sinfo->si_code;
+
+ /* Restore permissions in order to continue */
+ switch (fcode) {
+ case SEGV_ACCERR:
+ if (mprotect(insns, pgsize, PROT_READ | PROT_WRITE)) {
+ perror("mprotect");
+ goto fail;
+ }
+ break;
+ case SEGV_PKUERR:
+ if (pkey != fpkey)
+ goto fail;
+
+ if (ftype == PKEY_DISABLE_ACCESS) {
+ pkey_set_rights(fpkey, 0);
+ } else if (ftype == 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)) {
+ perror("mprotect");
+ goto fail;
+ }
+ } else {
+ goto fail;
+ }
+ break;
+ }
+
+ faults--;
+ return;
+
+fail:
+ /* Restore all page permissions to avoid repetitive faults */
+ if (mprotect(insns, pgsize, PROT_READ | PROT_WRITE | PROT_EXEC))
+ perror("mprotect");
+ if (sinfo->si_code == SEGV_PKUERR)
+ pkey_set_rights(pkey, 0);
+ faults = -1; /* Something unexpected happened */
+}
+
+static int pkeys_unsupported(void)
+{
+ bool using_hash = false;
+ char line[128];
+ int pkey;
+ FILE *f;
+
+ f = fopen("/proc/cpuinfo", "r");
+ FAIL_IF(!f);
+
+ /* Protection keys are currently supported on Hash MMU only */
+ while (fgets(line, sizeof(line), f)) {
+ if (strcmp(line, "MMU : Hash\n") == 0) {
+ using_hash = true;
+ break;
+ }
+ }
+
+ fclose(f);
+ SKIP_IF(!using_hash);
+
+ /* 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 act;
+ int pkey, ret, i;
+
+ ret = pkeys_unsupported();
+ if (ret)
+ return ret;
+
+ /* Setup signal handler */
+ act.sa_handler = 0;
+ act.sa_sigaction = segv_handler;
+ FAIL_IF(sigprocmask(SIG_SETMASK, 0, &act.sa_mask) != 0);
+ act.sa_flags = SA_SIGINFO;
+ act.sa_restorer = 0;
+ FAIL_IF(sigaction(SIGSEGV, &act, NULL) != 0);
+
+ /* Setup executable region */
+ pgsize = sysconf(_SC_PAGESIZE);
+ 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 = 0; i < numinsns - 1; i++)
+ insns[i] = 0x60000000; /* nop */
+
+ /*
+ * Later, to jump to the executable region, we use a linked
+ * branch which sets the return address automatically in LR.
+ * Use that to return back.
+ */
+ insns[numinsns - 1] = 0x4e800020; /* blr */
+
+ /* Allocate a pkey that restricts execution */
+ pkey = sys_pkey_alloc(0, PKEY_DISABLE_EXECUTE);
+ FAIL_IF(pkey < 0);
+
+ /*
+ * Pick a random instruction address from the executable
+ * region.
+ */
+ srand(time(NULL));
+ faddr = &insns[rand() % (numinsns - 1)];
+
+ /* The following two cases will avoid SEGV_PKUERR */
+ ftype = -1;
+ fpkey = -1;
+
+ /*
+ * Read an instruction word from the address when AMR bits
+ * are not set.
+ *
+ * This should not generate a fault as having PROT_EXEC
+ * implicitly allows reads. The pkey currently restricts
+ * execution only based on the IAMR bits. The AMR bits are
+ * cleared.
+ */
+ faults = 0;
+ FAIL_IF(sys_pkey_mprotect(insns, pgsize, PROT_EXEC, pkey) != 0);
+ printf("read from %p, pkey is execute-disabled\n", (void *) faddr);
+ i = *faddr;
+ FAIL_IF(faults != 0);
+
+ /*
+ * Write an instruction word to the address when AMR bits
+ * are not set.
+ *
+ * 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.
+ */
+ faults = 1;
+ FAIL_IF(sys_pkey_mprotect(insns, pgsize, PROT_EXEC, pkey) != 0);
+ printf("write to %p, pkey is execute-disabled\n", (void *) faddr);
+ *faddr = 0x60000000; /* nop */
+ FAIL_IF(faults != 0 || fcode != SEGV_ACCERR);
+
+ /* The following three cases will generate SEGV_PKUERR */
+ ftype = PKEY_DISABLE_ACCESS;
+ fpkey = pkey;
+
+ /*
+ * Read an instruction word from the address when AMR bits
+ * are set.
+ *
+ * This should generate a pkey fault based on AMR bits only
+ * as having PROT_EXEC implicitly allows reads.
+ */
+ 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 *) faddr);
+ pkey_set_rights(pkey, PKEY_DISABLE_ACCESS);
+ i = *faddr;
+ FAIL_IF(faults != 0 || fcode != SEGV_PKUERR);
+
+ /*
+ * Write an instruction word to the address when AMR bits
+ * are set.
+ *
+ * This should generate two faults. First, a pkey fault based
+ * on AMR bits and then an access fault based on PROT_EXEC.
+ */
+ 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 *) faddr);
+ pkey_set_rights(pkey, PKEY_DISABLE_ACCESS);
+ *faddr = 0x60000000; /* nop */
+ FAIL_IF(faults != 0 || fcode != SEGV_ACCERR);
+
+ /*
+ * Jump to the executable region. This should generate a pkey
+ * fault based on IAMR bits. AMR bits will not affect execution.
+ */
+ faddr = insns;
+ ftype = PKEY_DISABLE_EXECUTE;
+ fpkey = pkey;
+ faults = 1;
+ FAIL_IF(sys_pkey_mprotect(insns, pgsize, PROT_EXEC, pkey) != 0);
+ pkey_set_rights(pkey, PKEY_DISABLE_ACCESS);
+ printf("execute at %p, ", (void *) faddr);
+ printf("pkey is execute-disabled, access-disabled\n");
+
+ /* Branch into the executable region */
+ asm volatile("mtctr %0" : : "r"((unsigned long) insns));
+ asm volatile("bctrl");
+ FAIL_IF(faults != 0 || fcode != SEGV_PKUERR);
+
+ /* Cleanup */
+ munmap((void *) insns, pgsize);
+ sys_pkey_free(pkey);
+
+ return 0;
+}
+
+int main(void)
+{
+ test_harness(test, "pkey_exec_prot");
+}
--
2.25.1
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