linux-kernel - [PATCH 4/9] ARC: mm: do_page_fault refactor #3: tidyup vma access permission code

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Date:   Tue, 14 May 2019 17:29:31 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     <linux-snps-arc@...ts.infradead.org>
CC:     <paltsev@...opsys.com>, <linux-kernel@...r.kernel.org>,
        Vineet Gupta <Vineet.Gupta1@...opsys.com>
Subject: [PATCH 4/9] ARC: mm: do_page_fault refactor #3: tidyup vma access permission code

The coding pattern to NOT intialize variables at declaration time but
rather near code which makes us eof them makes it much easier to grok
the overall logic, specially when the init is not simply 0 or 1

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
---
 arch/arc/mm/fault.c | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index f1175685d914..ae890a8d5ebf 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -67,9 +67,9 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
 	struct task_struct *tsk = current;
 	struct mm_struct *mm = tsk->mm;
 	int si_code = SEGV_MAPERR;
+	unsigned int write = 0, exec = 0, mask;
 	vm_fault_t fault;
-	int write = regs->ecr_cause & ECR_C_PROTV_STORE;  /* ST/EX */
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags;
 
 	/*
 	 * NOTE! We MUST NOT take any locks for this case. We may
@@ -91,8 +91,18 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
 	if (faulthandler_disabled() || !mm)
 		goto no_context;
 
+	if (regs->ecr_cause & ECR_C_PROTV_STORE)	/* ST/EX */
+		write = 1;
+	else if ((regs->ecr_vec == ECR_V_PROTV) &&
+	         (regs->ecr_cause == ECR_C_PROTV_INST_FETCH))
+		exec = 1;
+
+	flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
+	if (write)
+		flags |= FAULT_FLAG_WRITE;
+
 retry:
 	down_read(&mm->mmap_sem);
 
@@ -105,24 +115,17 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
 	}
 
 	/*
-	 * Ok, we have a good vm_area for this memory access, so
-	 * we can handle it..
+	 * vm_area is good, now check permissions for this memory access
 	 */
-	si_code = SEGV_ACCERR;
-
-	/* Handle protection violation, execute on heap or stack */
-
-	if ((regs->ecr_vec == ECR_V_PROTV) &&
-	    (regs->ecr_cause == ECR_C_PROTV_INST_FETCH))
+	mask = VM_READ;
+	if (write)
+		mask = VM_WRITE;
+	if (exec)
+		mask = VM_EXEC;
+
+	if (!(vma->vm_flags & mask)) {
+		si_code = SEGV_ACCERR;
 		goto bad_area;
-
-	if (write) {
-		if (!(vma->vm_flags & VM_WRITE))
-			goto bad_area;
-		flags |= FAULT_FLAG_WRITE;
-	} else {
-		if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
-			goto bad_area;
 	}
 
 	/*
-- 
2.7.4