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Date: Wed, 29 Sep 2010 11:28:08 -0700
From: David Daney <ddaney@...iumnetworks.com>
To: Al Viro <viro@....linux.org.uk>
CC: ralf@...ux-mips.org, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org,
"Maciej W. Rozycki" <macro@...ux-mips.org>
Subject: Re: [PATCH 3/5] mips: sanitize restart logics
On 09/28/2010 10:50 AM, Al Viro wrote:
>
> Put the original syscall number into ->regs[0] when we leave syscall
> with error. Use it in restart logics. Everything else will have
> it 0 since we pass through SAVE_SOME on all the ways in. Note that
> in places like bad_stack and inllegal_syscall we leave it 0 - it's
> not restartable.
>
IIRC Userspace getcontext/setcontext rely on regs[0] having a value of
zero in the when the signal handlers are invoked.
I haven't fully traced through the code, but I hope that this
'invariant' holds both before and after this patch. I think Maciej did
the work on getcontext/setcontext, he may know for sure what the
requirements are.
David Daney
> Signed-off-by: Al Viro<viro@...iv.linux.org.uk>
> ---
> arch/mips/kernel/branch.c | 1 -
> arch/mips/kernel/scall32-o32.S | 9 ++++-----
> arch/mips/kernel/scall64-64.S | 7 ++++---
> arch/mips/kernel/scall64-n32.S | 6 ++++--
> arch/mips/kernel/scall64-o32.S | 7 ++++---
> arch/mips/kernel/signal.c | 37 ++++++++++++++++++-------------------
> arch/mips/kernel/unaligned.c | 2 --
> 7 files changed, 34 insertions(+), 35 deletions(-)
>
> diff --git a/arch/mips/kernel/branch.c b/arch/mips/kernel/branch.c
> index 0176ed0..32103cc 100644
> --- a/arch/mips/kernel/branch.c
> +++ b/arch/mips/kernel/branch.c
> @@ -40,7 +40,6 @@ int __compute_return_epc(struct pt_regs *regs)
> return -EFAULT;
> }
>
> - regs->regs[0] = 0;
> switch (insn.i_format.opcode) {
> /*
> * jr and jalr are in r_format format.
> diff --git a/arch/mips/kernel/scall32-o32.S b/arch/mips/kernel/scall32-o32.S
> index 17202bb..d3edb9f 100644
> --- a/arch/mips/kernel/scall32-o32.S
> +++ b/arch/mips/kernel/scall32-o32.S
> @@ -63,9 +63,9 @@ stack_done:
> sw t0, PT_R7(sp) # set error flag
> beqz t0, 1f
>
> + lw t1, PR_R2(sp) # syscall number
> negu v0 # error
> - sw v0, PT_R0(sp) # set flag for syscall
> - # restarting
> + sw t1, PT_R0(sp) # save it for syscall restarting
> 1: sw v0, PT_R2(sp) # result
>
> o32_syscall_exit:
> @@ -104,9 +104,9 @@ syscall_trace_entry:
> sw t0, PT_R7(sp) # set error flag
> beqz t0, 1f
>
> + lw t1, PT_R2(sp) # syscall number
> negu v0 # error
> - sw v0, PT_R0(sp) # set flag for syscall
> - # restarting
> + sw t1, PT_R0(sp) # save it for syscall restarting
> 1: sw v0, PT_R2(sp) # result
>
> j syscall_exit
> @@ -170,7 +170,6 @@ stackargs:
> */
> bad_stack:
> negu v0 # error
> - sw v0, PT_R0(sp)
> sw v0, PT_R2(sp)
> li t0, 1 # set error flag
> sw t0, PT_R7(sp)
> diff --git a/arch/mips/kernel/scall64-64.S b/arch/mips/kernel/scall64-64.S
> index a8a6c59..eb0bb73 100644
> --- a/arch/mips/kernel/scall64-64.S
> +++ b/arch/mips/kernel/scall64-64.S
> @@ -66,9 +66,9 @@ NESTED(handle_sys64, PT_SIZE, sp)
> sd t0, PT_R7(sp) # set error flag
> beqz t0, 1f
>
> + ld t1, PT_R2(sp) # syscall number
> dnegu v0 # error
> - sd v0, PT_R0(sp) # set flag for syscall
> - # restarting
> + sd t1, PT_R0(sp) # save it for syscall restarting
> 1: sd v0, PT_R2(sp) # result
>
> n64_syscall_exit:
> @@ -109,8 +109,9 @@ syscall_trace_entry:
> sd t0, PT_R7(sp) # set error flag
> beqz t0, 1f
>
> + ld t1, PT_R2(sp) # syscall number
> dnegu v0 # error
> - sd v0, PT_R0(sp) # set flag for syscall restarting
> + sd t1, PT_R0(sp) # save it for syscall restarting
> 1: sd v0, PT_R2(sp) # result
>
> j syscall_exit
> diff --git a/arch/mips/kernel/scall64-n32.S b/arch/mips/kernel/scall64-n32.S
> index a3d6613..4da3faf 100644
> --- a/arch/mips/kernel/scall64-n32.S
> +++ b/arch/mips/kernel/scall64-n32.S
> @@ -65,8 +65,9 @@ NESTED(handle_sysn32, PT_SIZE, sp)
> sd t0, PT_R7(sp) # set error flag
> beqz t0, 1f
>
> + ld t1, PT_R2(sp) # syscall number
> dnegu v0 # error
> - sd v0, PT_R0(sp) # set flag for syscall restarting
> + sd t1, PT_R0(sp) # save it for syscall restarting
> 1: sd v0, PT_R2(sp) # result
>
> local_irq_disable # make sure need_resched and
> @@ -106,8 +107,9 @@ n32_syscall_trace_entry:
> sd t0, PT_R7(sp) # set error flag
> beqz t0, 1f
>
> + ld t1, PT_R2(sp) # syscall number
> dnegu v0 # error
> - sd v0, PT_R0(sp) # set flag for syscall restarting
> + sd t1, PT_R0(sp) # save it for syscall restarting
> 1: sd v0, PT_R2(sp) # result
>
> j syscall_exit
> diff --git a/arch/mips/kernel/scall64-o32.S b/arch/mips/kernel/scall64-o32.S
> index 813689e..7ce0a36 100644
> --- a/arch/mips/kernel/scall64-o32.S
> +++ b/arch/mips/kernel/scall64-o32.S
> @@ -93,8 +93,9 @@ NESTED(handle_sys, PT_SIZE, sp)
> sd t0, PT_R7(sp) # set error flag
> beqz t0, 1f
>
> + ld t1, PT_R2(sp) # syscall number
> dnegu v0 # error
> - sd v0, PT_R0(sp) # flag for syscall restarting
> + sd t1, PT_R0(sp) # save it for syscall restarting
> 1: sd v0, PT_R2(sp) # result
>
> o32_syscall_exit:
> @@ -142,8 +143,9 @@ trace_a_syscall:
> sd t0, PT_R7(sp) # set error flag
> beqz t0, 1f
>
> + ld t1, PT_R2(sp) # syscall number
> dnegu v0 # error
> - sd v0, PT_R0(sp) # set flag for syscall restarting
> + sd t1, PT_R0(sp) # save it for syscall restarting
> 1: sd v0, PT_R2(sp) # result
>
> j syscall_exit
> @@ -155,7 +157,6 @@ trace_a_syscall:
> */
> bad_stack:
> dnegu v0 # error
> - sd v0, PT_R0(sp)
> sd v0, PT_R2(sp)
> li t0, 1 # set error flag
> sd t0, PT_R7(sp)
> diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
> index b3273ae..604f077 100644
> --- a/arch/mips/kernel/signal.c
> +++ b/arch/mips/kernel/signal.c
> @@ -550,23 +550,26 @@ static int handle_signal(unsigned long sig, siginfo_t *info,
> struct mips_abi *abi = current->thread.abi;
> void *vdso = current->mm->context.vdso;
>
> - switch(regs->regs[0]) {
> - case ERESTART_RESTARTBLOCK:
> - case ERESTARTNOHAND:
> - regs->regs[2] = EINTR;
> - break;
> - case ERESTARTSYS:
> - if (!(ka->sa.sa_flags& SA_RESTART)) {
> + if (regs->regs[0]) {
> + switch(regs->regs[2]) {
> + case ERESTART_RESTARTBLOCK:
> + case ERESTARTNOHAND:
> regs->regs[2] = EINTR;
> break;
> + case ERESTARTSYS:
> + if (!(ka->sa.sa_flags& SA_RESTART)) {
> + regs->regs[2] = EINTR;
> + break;
> + }
> + /* fallthrough */
> + case ERESTARTNOINTR:
> + regs->regs[7] = regs->regs[26];
> + regs->regs[2] = regs->regs[0];
> + regs->cp0_epc -= 4;
> }
> - /* fallthrough */
> - case ERESTARTNOINTR: /* Userland will reload $v0. */
> - regs->regs[7] = regs->regs[26];
> - regs->cp0_epc -= 8;
> - }
>
> - regs->regs[0] = 0; /* Don't deal with this again. */
> + regs->regs[0] = 0; /* Don't deal with this again. */
> + }
>
> if (sig_uses_siginfo(ka))
> ret = abi->setup_rt_frame(vdso + abi->rt_signal_return_offset,
> @@ -625,17 +628,13 @@ static void do_signal(struct pt_regs *regs)
> return;
> }
>
> - /*
> - * Who's code doesn't conform to the restartable syscall convention
> - * dies here!!! The li instruction, a single machine instruction,
> - * must directly be followed by the syscall instruction.
> - */
> if (regs->regs[0]) {
> if (regs->regs[2] == ERESTARTNOHAND ||
> regs->regs[2] == ERESTARTSYS ||
> regs->regs[2] == ERESTARTNOINTR) {
> + regs->regs[2] = regs->regs[0];
> regs->regs[7] = regs->regs[26];
> - regs->cp0_epc -= 8;
> + regs->cp0_epc -= 4;
> }
> if (regs->regs[2] == ERESTART_RESTARTBLOCK) {
> regs->regs[2] = current->thread.abi->restart;
> diff --git a/arch/mips/kernel/unaligned.c b/arch/mips/kernel/unaligned.c
> index 69b039c..33d5a5c 100644
> --- a/arch/mips/kernel/unaligned.c
> +++ b/arch/mips/kernel/unaligned.c
> @@ -109,8 +109,6 @@ static void emulate_load_store_insn(struct pt_regs *regs,
> unsigned long value;
> unsigned int res;
>
> - regs->regs[0] = 0;
> -
> /*
> * This load never faults.
> */
--
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