Commit 1addb644 authored by Sandipan Das's avatar Sandipan Das Committed by Michael Ellerman

selftests/powerpc: Add test for execute-disabled pkeys

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: default avatarSandipan Das <sandipan@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200604125610.649668-4-sandipan@linux.ibm.com
parent c405b738
......@@ -8,3 +8,4 @@ wild_bctr
large_vm_fork_separation
bad_accesses
tlbie_test
pkey_exec_prot
......@@ -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
......
// 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");
}
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