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Subject: Re: [PATCH v2 2/2] powerpc: use probe_user_read()
To:     Christophe Leroy <christophe.leroy@c-s.fr>,
        Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Mike Rapoport <rppt@linux.ibm.com>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-mm@kvack.org
References: <0b0db24e18063076e9d9f4e376994af83da05456.1546932949.git.christophe.leroy@c-s.fr>
 <e939991366b784ef13c7afcab51749e3b46327ac.1546932949.git.christophe.leroy@c-s.fr>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <8a52b522-7b9d-e3d4-9c04-98292db11d85@redhat.com>
Date:   Tue, 8 Jan 2019 10:04:28 +0100
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In-Reply-To: <e939991366b784ef13c7afcab51749e3b46327ac.1546932949.git.christophe.leroy@c-s.fr>
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Sender: linux-kernel-owner@vger.kernel.org
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On 08.01.19 08:37, Christophe Leroy wrote:
> Instead of opencoding, use probe_user_read() to failessly
> read a user location.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>  v2: Using probe_user_read() instead of probe_user_address()
> 
>  arch/powerpc/kernel/process.c   | 12 +-----------
>  arch/powerpc/mm/fault.c         |  6 +-----
>  arch/powerpc/perf/callchain.c   | 20 +++-----------------
>  arch/powerpc/perf/core-book3s.c |  8 +-------
>  arch/powerpc/sysdev/fsl_pci.c   | 10 ++++------
>  5 files changed, 10 insertions(+), 46 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index ce393df243aa..6a4b59d574c2 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -1298,16 +1298,6 @@ void show_user_instructions(struct pt_regs *regs)
>  
>  	pc = regs->nip - (NR_INSN_TO_PRINT * 3 / 4 * sizeof(int));
>  
> -	/*
> -	 * Make sure the NIP points at userspace, not kernel text/data or
> -	 * elsewhere.
> -	 */
> -	if (!__access_ok(pc, NR_INSN_TO_PRINT * sizeof(int), USER_DS)) {
> -		pr_info("%s[%d]: Bad NIP, not dumping instructions.\n",
> -			current->comm, current->pid);
> -		return;
> -	}
> -
>  	seq_buf_init(&s, buf, sizeof(buf));
>  
>  	while (n) {
> @@ -1318,7 +1308,7 @@ void show_user_instructions(struct pt_regs *regs)
>  		for (i = 0; i < 8 && n; i++, n--, pc += sizeof(int)) {
>  			int instr;
>  
> -			if (probe_kernel_address((const void *)pc, instr)) {
> +			if (probe_user_read(&instr, (void __user *)pc, sizeof(instr))) {
>  				seq_buf_printf(&s, "XXXXXXXX ");
>  				continue;
>  			}
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 887f11bcf330..ec74305fa330 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -276,12 +276,8 @@ static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,
>  		if ((flags & FAULT_FLAG_WRITE) && (flags & FAULT_FLAG_USER) &&
>  		    access_ok(nip, sizeof(*nip))) {
>  			unsigned int inst;
> -			int res;
>  
> -			pagefault_disable();
> -			res = __get_user_inatomic(inst, nip);
> -			pagefault_enable();
> -			if (!res)
> +			if (!probe_user_read(&inst, nip, sizeof(inst)))
>  				return !store_updates_sp(inst);
>  			*must_retry = true;
>  		}
> diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
> index 0af051a1974e..0680efb2237b 100644
> --- a/arch/powerpc/perf/callchain.c
> +++ b/arch/powerpc/perf/callchain.c
> @@ -159,12 +159,8 @@ static int read_user_stack_64(unsigned long __user *ptr, unsigned long *ret)
>  	    ((unsigned long)ptr & 7))
>  		return -EFAULT;
>  
> -	pagefault_disable();
> -	if (!__get_user_inatomic(*ret, ptr)) {
> -		pagefault_enable();
> +	if (!probe_user_read(ret, ptr, sizeof(*ret)))
>  		return 0;
> -	}
> -	pagefault_enable();
>  
>  	return read_user_stack_slow(ptr, ret, 8);
>  }
> @@ -175,12 +171,8 @@ static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
>  	    ((unsigned long)ptr & 3))
>  		return -EFAULT;
>  
> -	pagefault_disable();
> -	if (!__get_user_inatomic(*ret, ptr)) {
> -		pagefault_enable();
> +	if (!probe_user_read(ret, ptr, sizeof(*ret)))
>  		return 0;
> -	}
> -	pagefault_enable();
>  
>  	return read_user_stack_slow(ptr, ret, 4);
>  }
> @@ -307,17 +299,11 @@ static inline int current_is_64bit(void)
>   */
>  static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
>  {
> -	int rc;
> -
>  	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
>  	    ((unsigned long)ptr & 3))
>  		return -EFAULT;
>  
> -	pagefault_disable();
> -	rc = __get_user_inatomic(*ret, ptr);
> -	pagefault_enable();
> -
> -	return rc;
> +	return probe_user_read(ret, ptr, sizeof(*ret));
>  }
>  
>  static inline void perf_callchain_user_64(struct perf_callchain_entry_ctx *entry,
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index b0723002a396..4b64ddf0db68 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -416,7 +416,6 @@ static void power_pmu_sched_task(struct perf_event_context *ctx, bool sched_in)
>  static __u64 power_pmu_bhrb_to(u64 addr)
>  {
>  	unsigned int instr;
> -	int ret;
>  	__u64 target;
>  
>  	if (is_kernel_addr(addr)) {
> @@ -427,13 +426,8 @@ static __u64 power_pmu_bhrb_to(u64 addr)
>  	}
>  
>  	/* Userspace: need copy instruction here then translate it */
> -	pagefault_disable();
> -	ret = __get_user_inatomic(instr, (unsigned int __user *)addr);
> -	if (ret) {
> -		pagefault_enable();
> +	if (probe_user_read(&instr, (unsigned int __user *)addr, sizeof(instr)))
>  		return 0;
> -	}
> -	pagefault_enable();
>  
>  	target = branch_target(&instr);
>  	if ((!target) || (instr & BRANCH_ABSOLUTE))
> diff --git a/arch/powerpc/sysdev/fsl_pci.c b/arch/powerpc/sysdev/fsl_pci.c
> index 918be816b097..c8a1b26489f5 100644
> --- a/arch/powerpc/sysdev/fsl_pci.c
> +++ b/arch/powerpc/sysdev/fsl_pci.c
> @@ -1068,13 +1068,11 @@ int fsl_pci_mcheck_exception(struct pt_regs *regs)
>  	addr += mfspr(SPRN_MCAR);
>  
>  	if (is_in_pci_mem_space(addr)) {
> -		if (user_mode(regs)) {
> -			pagefault_disable();
> -			ret = get_user(inst, (__u32 __user *)regs->nip);
> -			pagefault_enable();
> -		} else {
> +		if (user_mode(regs))
> +			ret = probe_user_read(&inst, (void __user *)regs->nip,
> +					      sizeof(inst));

What about also adding probe_user_address ?

> +		else
>  			ret = probe_kernel_address((void *)regs->nip, inst);
> -		}
>  
>  		if (!ret && mcheck_handle_load(regs, inst)) {
>  			regs->nip += 4;
> 


-- 

Thanks,

David / dhildenb