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Date:   Mon, 28 May 2018 21:30:03 +0100
From:   Al Viro <viro@ZenIV.linux.org.uk>
To:     Mathieu Malaterre <malat@debian.org>
Cc:     linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH][RFC] [powerpc] arch_ptrace() uses of access_ok() are
 pointless
Message-ID: <20180528203002.GD30522@ZenIV.linux.org.uk>
References: <20180527223403.GT30522@ZenIV.linux.org.uk>
 <CA+7wUswhpVRQ4yECc-Zh9djHxiT=9-ALuP7_=mfLMtU-NXDnfg@mail.gmail.com>
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> Maybe this is just an RFC, but:
> 
>   CALL    ../arch/powerpc/kernel/systbl_chk.sh
> ../arch/powerpc/kernel/ptrace.c: In function ‘arch_ptrace’:
> ../arch/powerpc/kernel/ptrace.c:3086:4: error: expected ‘)’ before ‘return’
>     return -EFAULT;
>     ^~~~~~

and the same a few lines later.  What's more, those 'unlikely' are pointless
there.  Fixed variant follows; only build-tested, though.

make it use copy_{from,to}_user(), rather than access_ok() +
__copy_...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 arch/powerpc/kernel/ptrace.c | 22 +++++++---------------
 1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index d23cf632edf0..f557322621e0 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -3081,27 +3081,19 @@ long arch_ptrace(struct task_struct *child, long request,
 #endif /* CONFIG_HAVE_HW_BREAKPOINT */
 #endif /* CONFIG_PPC_ADV_DEBUG_REGS */
 
-		if (!access_ok(VERIFY_WRITE, datavp,
-			       sizeof(struct ppc_debug_info)))
+		if (copy_to_user(datavp, &dbginfo,
+				     sizeof(struct ppc_debug_info)))
 			return -EFAULT;
-		ret = __copy_to_user(datavp, &dbginfo,
-				     sizeof(struct ppc_debug_info)) ?
-		      -EFAULT : 0;
-		break;
+		return 0;
 	}
 
 	case PPC_PTRACE_SETHWDEBUG: {
 		struct ppc_hw_breakpoint bp_info;
 
-		if (!access_ok(VERIFY_READ, datavp,
-			       sizeof(struct ppc_hw_breakpoint)))
-			return -EFAULT;
-		ret = __copy_from_user(&bp_info, datavp,
-				       sizeof(struct ppc_hw_breakpoint)) ?
-		      -EFAULT : 0;
-		if (!ret)
-			ret = ppc_set_hwdebug(child, &bp_info);
-		break;
+		if (copy_from_user(&bp_info, datavp,
+				       sizeof(struct ppc_hw_breakpoint)))
+		      return -EFAULT;
+		return ppc_set_hwdebug(child, &bp_info);
 	}
 
 	case PPC_PTRACE_DELHWDEBUG: {
-- 
2.11.0