[PATCH 4/4] powerpc: Use trap metadata to prevent double restart rather than zeroing trap
Nicholas Piggin
npiggin at gmail.com
Tue Apr 21 12:19:55 AEST 2020
It's not very nice to zero trap for this, because then system calls no
longer have TRAP_IS_SYSCALL(regs) invariant, and we can't distinguish
between sc and scv system calls (in a later patch).
Take one last unused bit from the low bits of the pt_regs.trap word for
this instead. There is not a really good reason why it should be in trap
as opposed to another field, but trap has some concept of flags and it
exists. Ideally I think we would move trap to 2-byte field and have 2
more bytes available independently.
Add a selftests case for this, which can be seen to fail if
TRAP_NORESTART is defined to false.
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
arch/powerpc/include/asm/ptrace.h | 15 +-
arch/powerpc/kernel/signal.c | 7 +-
arch/powerpc/kernel/signal_32.c | 2 +-
arch/powerpc/kernel/signal_64.c | 10 +-
.../testing/selftests/powerpc/signal/Makefile | 2 +-
.../powerpc/signal/sig_sc_double_restart.c | 174 ++++++++++++++++++
6 files changed, 194 insertions(+), 16 deletions(-)
create mode 100644 tools/testing/selftests/powerpc/signal/sig_sc_double_restart.c
diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
index 5eb249c725bd..5ee7eb128fb9 100644
--- a/arch/powerpc/include/asm/ptrace.h
+++ b/arch/powerpc/include/asm/ptrace.h
@@ -184,13 +184,13 @@ extern int ptrace_put_reg(struct task_struct *task, int regno,
#ifdef __powerpc64__
#ifdef CONFIG_PPC_BOOK3S
-#define TRAP(regs) ((regs)->trap)
-#define SET_TRAP(regs, val) ((regs)->trap = (val))
+#define TRAP(regs) ((regs)->trap & ~0x10)
+#define SET_TRAP(regs, val) ((regs)->trap = ((regs)->trap & 0x10) | ((val) & ~0x10))
#define FULL_REGS(regs) true
#define SET_FULL_REGS(regs) do { } while (0)
#else
-#define TRAP(regs) ((regs)->trap & ~0x1)
-#define SET_TRAP(regs, val) ((regs)->trap = ((regs)->trap & 0x1) | ((val) & ~0x1))
+#define TRAP(regs) ((regs)->trap & ~0x11)
+#define SET_TRAP(regs, val) ((regs)->trap = ((regs)->trap & 0x11) | ((val) & ~0x11))
#define FULL_REGS(regs) (((regs)->trap & 1) == 0)
#define SET_FULL_REGS(regs) ((regs)->trap |= 1)
#endif
@@ -204,8 +204,8 @@ extern int ptrace_put_reg(struct task_struct *task, int regno,
* On 4xx we use the next bit to indicate whether the exception
* is a critical exception (1 means it is).
*/
-#define TRAP(regs) ((regs)->trap & ~0xF)
-#define SET_TRAP(regs, val) ((regs)->trap = ((regs)->trap & 0xF) | ((val) & ~0xF))
+#define TRAP(regs) ((regs)->trap & ~0x1F)
+#define SET_TRAP(regs, val) ((regs)->trap = ((regs)->trap & 0x1F) | ((val) & ~0x1F))
#define FULL_REGS(regs) (((regs)->trap & 1) == 0)
#define SET_FULL_REGS(regs) ((regs)->trap |= 1)
#define IS_CRITICAL_EXC(regs) (((regs)->trap & 2) != 0)
@@ -219,6 +219,9 @@ do { \
} while (0)
#endif /* __powerpc64__ */
+#define TRAP_NORESTART(regs) (((regs)->trap & 16) == 16)
+#define SET_TRAP_NORESTART(regs) ((regs)->trap |= 16)
+
#define arch_has_single_step() (1)
#ifndef CONFIG_BOOK3S_601
#define arch_has_block_step() (true)
diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
index 4b74eef1d881..0de314075a8f 100644
--- a/arch/powerpc/kernel/signal.c
+++ b/arch/powerpc/kernel/signal.c
@@ -201,6 +201,9 @@ static void check_syscall_restart(struct pt_regs *regs, struct k_sigaction *ka,
if (!TRAP_IS_SYSCALL(regs))
return;
+ if (TRAP_NORESTART(regs))
+ return;
+
/* error signalled ? */
if (!(regs->ccr & 0x10000000))
return;
@@ -258,7 +261,7 @@ static void do_signal(struct task_struct *tsk)
if (ksig.sig <= 0) {
/* No signal to deliver -- put the saved sigmask back */
restore_saved_sigmask();
- tsk->thread.regs->trap = 0;
+ SET_TRAP_NORESTART(tsk->thread.regs);
return; /* no signals delivered */
}
@@ -285,7 +288,7 @@ static void do_signal(struct task_struct *tsk)
ret = handle_rt_signal64(&ksig, oldset, tsk);
}
- tsk->thread.regs->trap = 0;
+ SET_TRAP_NORESTART(tsk->thread.regs);
signal_setup_done(ret, &ksig, test_thread_flag(TIF_SINGLESTEP));
}
diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 4f96d29a22bf..2970e1fd8d02 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -500,7 +500,7 @@ static long restore_user_regs(struct pt_regs *regs,
if (!sig)
save_r2 = (unsigned int)regs->gpr[2];
err = restore_general_regs(regs, sr);
- regs->trap = 0;
+ SET_TRAP_NORESTART(regs);
err |= __get_user(msr, &sr->mc_gregs[PT_MSR]);
if (!sig)
regs->gpr[2] = (unsigned long) save_r2;
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index adfde59cf4ba..1f6565dbe248 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -350,8 +350,8 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
err |= __get_user(regs->link, &sc->gp_regs[PT_LNK]);
err |= __get_user(regs->xer, &sc->gp_regs[PT_XER]);
err |= __get_user(regs->ccr, &sc->gp_regs[PT_CCR]);
- /* skip SOFTE */
- regs->trap = 0;
+ /* Don't allow userspace to set SOFTE */
+ SET_TRAP_NORESTART(regs);
err |= __get_user(regs->dar, &sc->gp_regs[PT_DAR]);
err |= __get_user(regs->dsisr, &sc->gp_regs[PT_DSISR]);
err |= __get_user(regs->result, &sc->gp_regs[PT_RESULT]);
@@ -472,10 +472,8 @@ static long restore_tm_sigcontexts(struct task_struct *tsk,
&sc->gp_regs[PT_XER]);
err |= __get_user(tsk->thread.ckpt_regs.ccr,
&sc->gp_regs[PT_CCR]);
-
- /* Don't allow userspace to set the trap value */
- regs->trap = 0;
-
+ /* Don't allow userspace to set SOFTE */
+ SET_TRAP_NORESTART(regs);
/* These regs are not checkpointed; they can go in 'regs'. */
err |= __get_user(regs->dar, &sc->gp_regs[PT_DAR]);
err |= __get_user(regs->dsisr, &sc->gp_regs[PT_DSISR]);
diff --git a/tools/testing/selftests/powerpc/signal/Makefile b/tools/testing/selftests/powerpc/signal/Makefile
index 932a032bf036..d6ae54663aed 100644
--- a/tools/testing/selftests/powerpc/signal/Makefile
+++ b/tools/testing/selftests/powerpc/signal/Makefile
@@ -1,5 +1,5 @@
# SPDX-License-Identifier: GPL-2.0
-TEST_GEN_PROGS := signal signal_tm sigfuz sigreturn_vdso
+TEST_GEN_PROGS := signal signal_tm sigfuz sigreturn_vdso sig_sc_double_restart
CFLAGS += -maltivec
$(OUTPUT)/signal_tm: CFLAGS += -mhtm
diff --git a/tools/testing/selftests/powerpc/signal/sig_sc_double_restart.c b/tools/testing/selftests/powerpc/signal/sig_sc_double_restart.c
new file mode 100644
index 000000000000..64732adf3d91
--- /dev/null
+++ b/tools/testing/selftests/powerpc/signal/sig_sc_double_restart.c
@@ -0,0 +1,174 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Test that a syscall does not get restarted twice.
+ *
+ * Based on Al's description, and a test for the bug fixed in this commit:
+ *
+ * commit 9a81c16b527528ad307843be5571111aa8d35a80
+ * Author: Al Viro <viro at zeniv.linux.org.uk>
+ * Date: Mon Sep 20 21:48:57 2010 +0100
+ *
+ * powerpc: fix double syscall restarts
+ *
+ * Make sigreturn zero regs->trap, make do_signal() do the same on all
+ * paths. As it is, signal interrupting e.g. read() from fd 512 (==
+ * ERESTARTSYS) with another signal getting unblocked when the first
+ * handler finishes will lead to restart one insn earlier than it ought
+ * to. Same for multiple signals with in-kernel handlers interrupting
+ * that sucker at the same time. Same for multiple signals of any kind
+ * interrupting that sucker on 64bit...
+ */
+#define _GNU_SOURCE
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <signal.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "utils.h"
+
+static void SIGUSR1_handler(int sig)
+{
+ kill(getpid(), SIGUSR2);
+ /*
+ * SIGUSR2 is blocked until the handler exits, at which point it will
+ * be raised again and think there is a restart to be done because the
+ * pending restarted syscall has 512 (ERESTARTSYS) in r3. The second
+ * restart will retreat NIP another 4 bytes to fail case branch.
+ */
+}
+
+static void SIGUSR2_handler(int sig)
+{
+}
+
+static ssize_t raw_read(int fd, void *buf, size_t count)
+{
+ register long nr asm("r0") = __NR_read;
+ register long _fd asm("r3") = fd;
+ register void *_buf asm("r4") = buf;
+ register size_t _count asm("r5") = count;
+
+ asm volatile(
+" b 0f \n"
+" b 1f \n"
+" 0: sc 0 \n"
+" bns 2f \n"
+" neg %0,%0 \n"
+" b 2f \n"
+" 1: \n"
+" li %0,%4 \n"
+" 2: \n"
+ : "+r"(_fd), "+r"(nr), "+r"(_buf), "+r"(_count)
+ : "i"(-ENOANO)
+ : "memory", "r6", "r7", "r8", "r9", "r10", "r11", "r12", "ctr", "cr0");
+
+ if (_fd < 0) {
+ errno = -_fd;
+ _fd = -1;
+ }
+
+ return _fd;
+}
+
+#define DATA "test 123"
+#define DLEN (strlen(DATA)+1)
+
+int test_restart(void)
+{
+ int pipefd[2];
+ pid_t pid;
+ char buf[512];
+
+ if (pipe(pipefd) == -1) {
+ perror("pipe");
+ exit(EXIT_FAILURE);
+ }
+
+ pid = fork();
+ if (pid == -1) {
+ perror("fork");
+ exit(EXIT_FAILURE);
+ }
+
+ if (pid == 0) { /* Child reads from pipe */
+ struct sigaction act;
+ int fd;
+
+ memset(&act, 0, sizeof(act));
+ sigaddset(&act.sa_mask, SIGUSR2);
+ act.sa_handler = SIGUSR1_handler;
+ act.sa_flags = SA_RESTART;
+ if (sigaction(SIGUSR1, &act, NULL) == -1) {
+ perror("sigaction");
+ exit(EXIT_FAILURE);
+ }
+
+ memset(&act, 0, sizeof(act));
+ act.sa_handler = SIGUSR2_handler;
+ act.sa_flags = SA_RESTART;
+ if (sigaction(SIGUSR2, &act, NULL) == -1) {
+ perror("sigaction");
+ exit(EXIT_FAILURE);
+ }
+
+ /* Let's get ERESTARTSYS into r3 */
+ while ((fd = dup(pipefd[0])) != 512) {
+ if (fd == -1) {
+ perror("dup");
+ exit(EXIT_FAILURE);
+ }
+ }
+
+ if (raw_read(fd, buf, 512) == -1) {
+ if (errno == ENOANO) {
+ fprintf(stderr, "Double restart moved restart before sc instruction.\n");
+ _exit(EXIT_FAILURE);
+ }
+ perror("read");
+ exit(EXIT_FAILURE);
+ }
+
+ if (strncmp(buf, DATA, DLEN)) {
+ fprintf(stderr, "bad test string %s\n", buf);
+ exit(EXIT_FAILURE);
+ }
+
+ return 0;
+
+ } else {
+ int wstatus;
+
+ usleep(100000); /* Hack to get reader waiting */
+ kill(pid, SIGUSR1);
+ usleep(100000);
+ if (write(pipefd[1], DATA, DLEN) != DLEN) {
+ perror("write");
+ exit(EXIT_FAILURE);
+ }
+ close(pipefd[0]);
+ close(pipefd[1]);
+ if (wait(&wstatus) == -1) {
+ perror("wait");
+ exit(EXIT_FAILURE);
+ }
+ if (!WIFEXITED(wstatus)) {
+ fprintf(stderr, "child exited abnormally\n");
+ exit(EXIT_FAILURE);
+ }
+
+ FAIL_IF(WEXITSTATUS(wstatus) != EXIT_SUCCESS);
+
+ return 0;
+ }
+}
+
+int main(void)
+{
+ test_harness_set_timeout(10);
+ return test_harness(test_restart, "sig sys restart");
+}
--
2.23.0
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