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powerpc: Use trap metadata to prevent double restart rather than zeroing trap

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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 changed to return false.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Make them static inlines]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200507121332.2233629-4-mpe@ellerman.id.au
This commit is contained in:
Nicholas Piggin
2020-05-07 22:13:32 +10:00
committed by Michael Ellerman
parent 912237ea16
commit 4e0e45b07d
6 changed files with 201 additions and 16 deletions
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7
arch/powerpc/kernel/signal.c
View File

@@ -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));
}

2
arch/powerpc/kernel/signal_32.c
View File

@@ -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;

10
arch/powerpc/kernel/signal_64.c
View File

@@ -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]);