[PATCH 5.12 234/242] s390/signal: switch to using vdso for sigreturn and syscall restart

Greg Kroah-Hartman
2021-07-15T19:20:52Z

From: Sven Schnelle <svens@linux.ibm.com>

commit df29a7440c4b5c65765c8f60396b3b13063e24e9 upstream.

with generic entry, there's a bug when it comes to restarting of signals.
The failing sequence is:

a) a signal is coming in, and no handler is registered, so the lower
part of arch_do_signal_or_restart() in arch/s390/kernel/signal.c
sets PIF_SYSCALL_RESTART.

b) a second signal gets pending while the kernel is still in the exit
loop, and for that one, a handler exists.

c) The first part of arch_do_signal_or_restart() is called. That part
calls handle_signal(), which sets up stack + registers for handling
the signal.

d) __do_syscall() in arch/s390/kernel/syscall.c checks for
PIF_SYSCALL_RESTART right before leaving to userspace. If it is set,
it restart's the syscall. However, the registers are already setup
for handling a signal from c). The syscall is now restarted with the
wrong arguments.

Change the code to:

- use vdso for syscall_restart() instead of PIF_SYSCALL_RESTART because
we cannot rewind and go back to userspace on s390 because the system call
number might be encoded in the svc instruction.
- for all other syscalls we rewind the PSW and return to userspace.

Cc: <stable@kernel.org> # v5.12+ d57778feb987: s390/vdso: always enable vdso
Cc: <stable@kernel.org> # v5.12+ 686341f2548b: s390/vdso64: add sigreturn,rt_sigreturn and restart_syscall
Cc: <stable@kernel.org> # v5.12+ 43e1f76b0b69: s390/vdso: rename VDSO64_LBASE to VDSO_LBASE
Cc: <stable@kernel.org> # v5.12+ 779df2248739: s390/vdso: add minimal compat vdso
Cc: <stable@kernel.org> # v5.12+
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/s390/kernel/compat_signal.c | 13 +++----------
arch/s390/kernel/process.c | 6 ++++++
arch/s390/kernel/signal.c | 39 ++++++++++++++++++---------------------
arch/s390/kernel/syscall.c | 4 ++++
4 files changed, 31 insertions(+), 31 deletions(-)

--- a/arch/s390/kernel/compat_signal.c
+++ b/arch/s390/kernel/compat_signal.c
@@ -28,6 +28,7 @@
#include <linux/uaccess.h>
#include <asm/lowcore.h>
#include <asm/switch_to.h>
+#include <asm/vdso.h>
#include "compat_linux.h"
#include "compat_ptrace.h"
#include "entry.h"
@@ -118,7 +119,6 @@ static int restore_sigregs32(struct pt_r
fpregs_load((_s390_fp_regs *) &user_sregs.fpregs, &current->thread.fpu);

clear_pt_regs_flag(regs, PIF_SYSCALL); /* No longer in a system call */
- clear_pt_regs_flag(regs, PIF_SYSCALL_RESTART);
return 0;
}

@@ -304,11 +304,7 @@ static int setup_frame32(struct ksignal
restorer = (unsigned long __force)
ksig->ka.sa.sa_restorer | PSW32_ADDR_AMODE;
} else {
- /* Signal frames without vectors registers are short ! */
- __u16 __user *svc = (void __user *) frame + frame_size - 2;
- if (__put_user(S390_SYSCALL_OPCODE | __NR_sigreturn, svc))
- return -EFAULT;
- restorer = (unsigned long __force) svc | PSW32_ADDR_AMODE;
+ restorer = VDSO32_SYMBOL(current, sigreturn);
}

/* Set up registers for signal handler */
@@ -371,10 +367,7 @@ static int setup_rt_frame32(struct ksign
restorer = (unsigned long __force)
ksig->ka.sa.sa_restorer | PSW32_ADDR_AMODE;
} else {
- __u16 __user *svc = &frame->svc_insn;
- if (__put_user(S390_SYSCALL_OPCODE | __NR_rt_sigreturn, svc))
- return -EFAULT;
- restorer = (unsigned long __force) svc | PSW32_ADDR_AMODE;
+ restorer = VDSO32_SYMBOL(current, rt_sigreturn);
}

/* Create siginfo on the signal stack */
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -166,6 +166,12 @@ int copy_thread(unsigned long clone_flag
p->thread.acrs[1] = (unsigned int)tls;
}
}
+ /*
+ * s390 stores the svc return address in arch_data when calling
+ * sigreturn()/restart_syscall() via vdso. 1 means no valid address
+ * stored.
+ */
+ p->restart_block.arch_data = 1;
return 0;
}

--- a/arch/s390/kernel/signal.c
+++ b/arch/s390/kernel/signal.c
@@ -32,6 +32,7 @@
#include <linux/uaccess.h>
#include <asm/lowcore.h>
#include <asm/switch_to.h>
+#include <asm/vdso.h>
#include "entry.h"

/*
@@ -171,7 +172,6 @@ static int restore_sigregs(struct pt_reg
fpregs_load(&user_sregs.fpregs, &current->thread.fpu);

clear_pt_regs_flag(regs, PIF_SYSCALL); /* No longer in a system call */
- clear_pt_regs_flag(regs, PIF_SYSCALL_RESTART);
return 0;
}

@@ -334,15 +334,10 @@ static int setup_frame(int sig, struct k

/* Set up to return from userspace. If provided, use a stub
already in userspace. */
- if (ka->sa.sa_flags & SA_RESTORER) {
+ if (ka->sa.sa_flags & SA_RESTORER)
restorer = (unsigned long) ka->sa.sa_restorer;
- } else {
- /* Signal frame without vector registers are short ! */
- __u16 __user *svc = (void __user *) frame + frame_size - 2;
- if (__put_user(S390_SYSCALL_OPCODE | __NR_sigreturn, svc))
- return -EFAULT;
- restorer = (unsigned long) svc;
- }
+ else
+ restorer = VDSO64_SYMBOL(current, sigreturn);

/* Set up registers for signal handler */
regs->gprs[14] = restorer;
@@ -397,14 +392,10 @@ static int setup_rt_frame(struct ksignal

/* Set up to return from userspace. If provided, use a stub
already in userspace. */
- if (ksig->ka.sa.sa_flags & SA_RESTORER) {
+ if (ksig->ka.sa.sa_flags & SA_RESTORER)
restorer = (unsigned long) ksig->ka.sa.sa_restorer;
- } else {
- __u16 __user *svc = &frame->svc_insn;
- if (__put_user(S390_SYSCALL_OPCODE | __NR_rt_sigreturn, svc))
- return -EFAULT;
- restorer = (unsigned long) svc;
- }
+ else
+ restorer = VDSO64_SYMBOL(current, rt_sigreturn);

/* Create siginfo on the signal stack */
if (copy_siginfo_to_user(&frame->info, &ksig->info))
@@ -501,7 +492,7 @@ void arch_do_signal_or_restart(struct pt
}
/* No longer in a system call */
clear_pt_regs_flag(regs, PIF_SYSCALL);
- clear_pt_regs_flag(regs, PIF_SYSCALL_RESTART);
+
rseq_signal_deliver(&ksig, regs);
if (is_compat_task())
handle_signal32(&ksig, oldset, regs);
@@ -517,14 +508,20 @@ void arch_do_signal_or_restart(struct pt
switch (regs->gprs[2]) {
case -ERESTART_RESTARTBLOCK:
/* Restart with sys_restart_syscall */
- regs->int_code = __NR_restart_syscall;
- fallthrough;
+ regs->gprs[2] = regs->orig_gpr2;
+ current->restart_block.arch_data = regs->psw.addr;
+ if (is_compat_task())
+ regs->psw.addr = VDSO32_SYMBOL(current, restart_syscall);
+ else
+ regs->psw.addr = VDSO64_SYMBOL(current, restart_syscall);
+ if (test_thread_flag(TIF_SINGLE_STEP))
+ clear_thread_flag(TIF_PER_TRAP);
+ break;
case -ERESTARTNOHAND:
case -ERESTARTSYS:
case -ERESTARTNOINTR:
- /* Restart system call with magic TIF bit. */
regs->gprs[2] = regs->orig_gpr2;
- set_pt_regs_flag(regs, PIF_SYSCALL_RESTART);
+ regs->psw.addr = __rewind_psw(regs->psw, regs->int_code >> 16);
if (test_thread_flag(TIF_SINGLE_STEP))
clear_thread_flag(TIF_PER_TRAP);
break;
--- a/arch/s390/kernel/syscall.c
+++ b/arch/s390/kernel/syscall.c
@@ -121,6 +121,10 @@ void do_syscall(struct pt_regs *regs)

regs->gprs[2] = nr;

+ if (nr == __NR_restart_syscall && !(current->restart_block.arch_data & 1)) {
+ regs->psw.addr = current->restart_block.arch_data;
+ current->restart_block.arch_data = 1;
+ }
nr = syscall_enter_from_user_mode_work(regs, nr);

/*