Commit 4e0e45b0 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

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



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: default avatarNicholas Piggin <npiggin@gmail.com>
[mpe: Make them static inlines]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200507121332.2233629-4-mpe@ellerman.id.au
parent 912237ea

arch/powerpc/include/asm/ptrace.h

+16 −6
Original line number Diff line number Diff line
@@ -182,13 +182,13 @@ extern int ptrace_put_reg(struct task_struct *task, int regno, 


#ifdef __powerpc64__

#ifdef CONFIG_PPC_BOOK3S

#define TRAP_FLAGS_MASK		0

#define TRAP(regs)		((regs)->trap)

#define TRAP_FLAGS_MASK		0x10

#define TRAP(regs)		((regs)->trap & ~TRAP_FLAGS_MASK)

#define FULL_REGS(regs)		true

#define SET_FULL_REGS(regs)	do { } while (0)

#else

#define TRAP_FLAGS_MASK		0x1

#define TRAP(regs)		((regs)->trap & ~0x1)

#define TRAP_FLAGS_MASK		0x11

#define TRAP(regs)		((regs)->trap & ~TRAP_FLAGS_MASK)

#define FULL_REGS(regs)		(((regs)->trap & 1) == 0)

#define SET_FULL_REGS(regs)	((regs)->trap |= 1)

#endif
@@ -202,8 +202,8 @@ 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_FLAGS_MASK		0xF

#define TRAP(regs)		((regs)->trap & ~0xF)

#define TRAP_FLAGS_MASK		0x1F

#define TRAP(regs)		((regs)->trap & ~TRAP_FLAGS_MASK)

#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)
@@ -227,6 +227,16 @@ static inline bool trap_is_syscall(struct pt_regs *regs) 
	return TRAP(regs) == 0xc00;

}



static inline bool trap_norestart(struct pt_regs *regs)

{

	return regs->trap & 0x10;

}



static inline void set_trap_norestart(struct pt_regs *regs)

{

	regs->trap |= 0x10;

}



#define arch_has_single_step()	(1)

#ifndef CONFIG_BOOK3S_601

#define arch_has_block_step()	(true)

arch/powerpc/kernel/signal.c

+5 −2
Original line number Diff line number Diff line
@@ -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));

}

arch/powerpc/kernel/signal_32.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

arch/powerpc/kernel/signal_64.c

+4 −6
Original line number Diff line number Diff line
@@ -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]);

tools/testing/selftests/powerpc/signal/Makefile

+1 −1
Original line number Diff line number Diff line 
# 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

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