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Subject: Re: [REVIEW][PATCH 08/22] signal/mips: Use force_sig_fault where
 appropriate
To:     "Eric W. Biederman" <ebiederm@xmission.com>,
        <linux-arch@vger.kernel.org>
CC:     <linux-kernel@vger.kernel.org>, Ralf Baechle <ralf@linux-mips.org>,
        James Hogan <jhogan@kernel.org>, <linux-mips@linux-mips.org>
References: <87604mhrnb.fsf@xmission.com>
 <20180420143811.9994-8-ebiederm@xmission.com>
From:   Matt Redfearn <matt.redfearn@mips.com>
Message-ID: <e0a5bde2-7817-3e05-1c8d-c8fa8f6aa5f2@mips.com>
Date:   Wed, 9 May 2018 16:14:40 +0100
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Hi Eric,

On 20/04/18 15:37, Eric W. Biederman wrote:
> Filling in struct siginfo before calling force_sig_info a tedious and
> error prone process, where once in a great while the wrong fields
> are filled out, and siginfo has been inconsistently cleared.
> 
> Simplify this process by using the helper force_sig_fault.  Which
> takes as a parameters all of the information it needs, ensures
> all of the fiddly bits of filling in struct siginfo are done properly
> and then calls force_sig_info.
> 
> In short about a 5 line reduction in code for every time force_sig_info
> is called, which makes the calling function clearer.
> 
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Cc: James Hogan <jhogan@kernel.org>
> Cc: linux-mips@linux-mips.org
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
>   arch/mips/kernel/traps.c | 65 ++++++++++++++----------------------------------
>   arch/mips/mm/fault.c     | 19 ++++----------
>   2 files changed, 23 insertions(+), 61 deletions(-)
> 
> diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
> index 967e9e4e795e..66ec4b0b484d 100644
> --- a/arch/mips/kernel/traps.c
> +++ b/arch/mips/kernel/traps.c
> @@ -699,17 +699,11 @@ static int simulate_sync(struct pt_regs *regs, unsigned int opcode)
>   asmlinkage void do_ov(struct pt_regs *regs)
>   {
>   	enum ctx_state prev_state;
> -	siginfo_t info;
> -
> -	clear_siginfo(&info);
> -	info.si_signo = SIGFPE;
> -	info.si_code = FPE_INTOVF;
> -	info.si_addr = (void __user *)regs->cp0_epc;
>   
>   	prev_state = exception_enter();
>   	die_if_kernel("Integer overflow", regs);
>   
> -	force_sig_info(SIGFPE, &info, current);
> +	force_sig_fault(SIGFPE, FPE_INTOVF, (void __user *)regs->cp0_epc, current);
>   	exception_exit(prev_state);
>   }
>   
> @@ -722,32 +716,27 @@ asmlinkage void do_ov(struct pt_regs *regs)
>   void force_fcr31_sig(unsigned long fcr31, void __user *fault_addr,
>   		     struct task_struct *tsk)
>   {
> -	struct siginfo si;
> -
> -	clear_siginfo(&si);
> -	si.si_addr = fault_addr;
> -	si.si_signo = SIGFPE;
> +	int si_code;

This is giving build errors in Linux next 
(https://storage.kernelci.org/next/master/next-20180509/mips/defconfig+kselftest/build.log)

si_code would have ended up as 0 before from the clear_siginfo(), but 
perhaps

int si_code = FPE_FLTUNK;

Would make a more sensible default?

Thanks,
Matt


>   
>   	if (fcr31 & FPU_CSR_INV_X)
> -		si.si_code = FPE_FLTINV;
> +		si_code = FPE_FLTINV;
>   	else if (fcr31 & FPU_CSR_DIV_X)
> -		si.si_code = FPE_FLTDIV;
> +		si_code = FPE_FLTDIV;
>   	else if (fcr31 & FPU_CSR_OVF_X)
> -		si.si_code = FPE_FLTOVF;
> +		si_code = FPE_FLTOVF;
>   	else if (fcr31 & FPU_CSR_UDF_X)
> -		si.si_code = FPE_FLTUND;
> +		si_code = FPE_FLTUND;
>   	else if (fcr31 & FPU_CSR_INE_X)
> -		si.si_code = FPE_FLTRES;
> +		si_code = FPE_FLTRES;
>   
> -	force_sig_info(SIGFPE, &si, tsk);
> +	force_sig_fault(SIGFPE, si_code, fault_addr, tsk);
>   }
>   
>   int process_fpemu_return(int sig, void __user *fault_addr, unsigned long fcr31)
>   {
> -	struct siginfo si;
> +	int si_code;
>   	struct vm_area_struct *vma;
>   
> -	clear_siginfo(&si);
>   	switch (sig) {
>   	case 0:
>   		return 0;
> @@ -757,23 +746,18 @@ int process_fpemu_return(int sig, void __user *fault_addr, unsigned long fcr31)
>   		return 1;
>   
>   	case SIGBUS:
> -		si.si_addr = fault_addr;
> -		si.si_signo = sig;
> -		si.si_code = BUS_ADRERR;
> -		force_sig_info(sig, &si, current);
> +		force_sig_fault(SIGBUS, BUS_ADRERR, fault_addr, current);
>   		return 1;
>   
>   	case SIGSEGV:
> -		si.si_addr = fault_addr;
> -		si.si_signo = sig;
>   		down_read(&current->mm->mmap_sem);
>   		vma = find_vma(current->mm, (unsigned long)fault_addr);
>   		if (vma && (vma->vm_start <= (unsigned long)fault_addr))
> -			si.si_code = SEGV_ACCERR;
> +			si_code = SEGV_ACCERR;
>   		else
> -			si.si_code = SEGV_MAPERR;
> +			si_code = SEGV_MAPERR;
>   		up_read(&current->mm->mmap_sem);
> -		force_sig_info(sig, &si, current);
> +		force_sig_fault(SIGSEGV, si_code, fault_addr, current);
>   		return 1;
>   
>   	default:
> @@ -896,10 +880,8 @@ asmlinkage void do_fpe(struct pt_regs *regs, unsigned long fcr31)
>   void do_trap_or_bp(struct pt_regs *regs, unsigned int code, int si_code,
>   	const char *str)
>   {
> -	siginfo_t info;
>   	char b[40];
>   
> -	clear_siginfo(&info);
>   #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
>   	if (kgdb_ll_trap(DIE_TRAP, str, regs, code, current->thread.trap_nr,
>   			 SIGTRAP) == NOTIFY_STOP)
> @@ -921,13 +903,9 @@ void do_trap_or_bp(struct pt_regs *regs, unsigned int code, int si_code,
>   	case BRK_DIVZERO:
>   		scnprintf(b, sizeof(b), "%s instruction in kernel code", str);
>   		die_if_kernel(b, regs);
> -		if (code == BRK_DIVZERO)
> -			info.si_code = FPE_INTDIV;
> -		else
> -			info.si_code = FPE_INTOVF;
> -		info.si_signo = SIGFPE;
> -		info.si_addr = (void __user *) regs->cp0_epc;
> -		force_sig_info(SIGFPE, &info, current);
> +		force_sig_fault(SIGFPE,
> +				code == BRK_DIVZERO ? FPE_INTDIV : FPE_INTOVF,
> +				(void __user *) regs->cp0_epc, current);
>   		break;
>   	case BRK_BUG:
>   		die_if_kernel("Kernel bug detected", regs);
> @@ -952,9 +930,7 @@ void do_trap_or_bp(struct pt_regs *regs, unsigned int code, int si_code,
>   		scnprintf(b, sizeof(b), "%s instruction in kernel code", str);
>   		die_if_kernel(b, regs);
>   		if (si_code) {
> -			info.si_signo = SIGTRAP;
> -			info.si_code = si_code;
> -			force_sig_info(SIGTRAP, &info, current);
> +			force_sig_fault(SIGTRAP, si_code, NULL,	current);
>   		} else {
>   			force_sig(SIGTRAP, current);
>   		}
> @@ -1506,13 +1482,8 @@ asmlinkage void do_mdmx(struct pt_regs *regs)
>    */
>   asmlinkage void do_watch(struct pt_regs *regs)
>   {
> -	siginfo_t info;
>   	enum ctx_state prev_state;
>   
> -	clear_siginfo(&info);
> -	info.si_signo = SIGTRAP;
> -	info.si_code = TRAP_HWBKPT;
> -
>   	prev_state = exception_enter();
>   	/*
>   	 * Clear WP (bit 22) bit of cause register so we don't loop
> @@ -1528,7 +1499,7 @@ asmlinkage void do_watch(struct pt_regs *regs)
>   	if (test_tsk_thread_flag(current, TIF_LOAD_WATCH)) {
>   		mips_read_watch_registers();
>   		local_irq_enable();
> -		force_sig_info(SIGTRAP, &info, current);
> +		force_sig_fault(SIGTRAP, TRAP_HWBKPT, NULL, current);
>   	} else {
>   		mips_clear_watch_registers();
>   		local_irq_enable();
> diff --git a/arch/mips/mm/fault.c b/arch/mips/mm/fault.c
> index 75392becd933..5f71f2b903b7 100644
> --- a/arch/mips/mm/fault.c
> +++ b/arch/mips/mm/fault.c
> @@ -42,7 +42,7 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
>   	struct task_struct *tsk = current;
>   	struct mm_struct *mm = tsk->mm;
>   	const int field = sizeof(unsigned long) * 2;
> -	siginfo_t info;
> +	int si_code;
>   	int fault;
>   	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
>   
> @@ -63,8 +63,7 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
>   		return;
>   #endif
>   
> -	clear_siginfo(&info);
> -	info.si_code = SEGV_MAPERR;
> +	si_code = SEGV_MAPERR;
>   
>   	/*
>   	 * We fault-in kernel-space virtual memory on-demand. The
> @@ -113,7 +112,7 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
>    * we can handle it..
>    */
>   good_area:
> -	info.si_code = SEGV_ACCERR;
> +	si_code = SEGV_ACCERR;
>   
>   	if (write) {
>   		if (!(vma->vm_flags & VM_WRITE))
> @@ -224,11 +223,7 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
>   			pr_cont("\n");
>   		}
>   		current->thread.trap_nr = (regs->cp0_cause >> 2) & 0x1f;
> -		info.si_signo = SIGSEGV;
> -		info.si_errno = 0;
> -		/* info.si_code has been set above */
> -		info.si_addr = (void __user *) address;
> -		force_sig_info(SIGSEGV, &info, tsk);
> +		force_sig_fault(SIGSEGV, si_code, (void __user *)address, tsk);
>   		return;
>   	}
>   
> @@ -284,11 +279,7 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
>   #endif
>   	current->thread.trap_nr = (regs->cp0_cause >> 2) & 0x1f;
>   	tsk->thread.cp0_badvaddr = address;
> -	info.si_signo = SIGBUS;
> -	info.si_errno = 0;
> -	info.si_code = BUS_ADRERR;
> -	info.si_addr = (void __user *) address;
> -	force_sig_info(SIGBUS, &info, tsk);
> +	force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address, tsk);
>   
>   	return;
>   #ifndef CONFIG_64BIT
>