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@linux.ibm.com ---
Previous versions can be found at v1: https://lore.kernel.org/linuxppc-dev/20200508162332.65316-1-sandipan@linux.i...
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"); +}