Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
Merge branch 'parisc-4.4-4' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux
Pull parisc system call restart fix from Helge Deller:
"The architectural design of parisc always uses two instructions to
call kernel syscalls (delayed branch feature). This means that the
instruction following the branch (located in the delay slot of the
branch instruction) is executed before control passes to the branch
destination.
Depending on which assembler instruction and how it is used in
usersapce in the delay slot, this sometimes made restarted syscalls
like futex() and poll() failing with -ENOSYS"
* 'parisc-4.4-4' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux:
parisc: Fix syscall restarts
+52
-12
+52
-12
arch/parisc/kernel/signal.c
+52
-12
arch/parisc/kernel/signal.c
···
435
435
regs->gr[28]);
436
436
}
437
437
438
+
/*
439
+
* Check how the syscall number gets loaded into %r20 within
440
+
* the delay branch in userspace and adjust as needed.
441
+
*/
442
+
443
+
static void check_syscallno_in_delay_branch(struct pt_regs *regs)
444
+
{
445
+
u32 opcode, source_reg;
446
+
u32 __user *uaddr;
447
+
int err;
448
+
449
+
/* Usually we don't have to restore %r20 (the system call number)
450
+
* because it gets loaded in the delay slot of the branch external
451
+
* instruction via the ldi instruction.
452
+
* In some cases a register-to-register copy instruction might have
453
+
* been used instead, in which case we need to copy the syscall
454
+
* number into the source register before returning to userspace.
455
+
*/
456
+
457
+
/* A syscall is just a branch, so all we have to do is fiddle the
458
+
* return pointer so that the ble instruction gets executed again.
459
+
*/
460
+
regs->gr[31] -= 8; /* delayed branching */
461
+
462
+
/* Get assembler opcode of code in delay branch */
463
+
uaddr = (unsigned int *) ((regs->gr[31] & ~3) + 4);
464
+
err = get_user(opcode, uaddr);
465
+
if (err)
466
+
return;
467
+
468
+
/* Check if delay branch uses "ldi int,%r20" */
469
+
if ((opcode & 0xffff0000) == 0x34140000)
470
+
return; /* everything ok, just return */
471
+
472
+
/* Check if delay branch uses "nop" */
473
+
if (opcode == INSN_NOP)
474
+
return;
475
+
476
+
/* Check if delay branch uses "copy %rX,%r20" */
477
+
if ((opcode & 0xffe0ffff) == 0x08000254) {
478
+
source_reg = (opcode >> 16) & 31;
479
+
regs->gr[source_reg] = regs->gr[20];
480
+
return;
481
+
}
482
+
483
+
pr_warn("syscall restart: %s (pid %d): unexpected opcode 0x%08x\n",
484
+
current->comm, task_pid_nr(current), opcode);
485
+
}
486
+
438
487
static inline void
439
488
syscall_restart(struct pt_regs *regs, struct k_sigaction *ka)
440
489
{
···
506
457
}
507
458
/* fallthrough */
508
459
case -ERESTARTNOINTR:
509
-
/* A syscall is just a branch, so all
510
-
* we have to do is fiddle the return pointer.
511
-
*/
512
-
regs->gr[31] -= 8; /* delayed branching */
460
+
check_syscallno_in_delay_branch(regs);
513
461
break;
514
462
}
515
463
}
···
556
510
}
557
511
case -ERESTARTNOHAND:
558
512
case -ERESTARTSYS:
559
-
case -ERESTARTNOINTR: {
560
-
/* Hooray for delayed branching. We don't
561
-
* have to restore %r20 (the system call
562
-
* number) because it gets loaded in the delay
563
-
* slot of the branch external instruction.
564
-
*/
565
-
regs->gr[31] -= 8;
513
+
case -ERESTARTNOINTR:
514
+
check_syscallno_in_delay_branch(regs);
566
515
return;
567
-
}
568
516
default:
569
517
break;
570
518
}