[v2,4/7] ARM: mm: print out correct page table entries

Commit Message

Kefeng Wang June 2, 2021, 7:02 a.m. UTC

Like commit 67ce16ec15ce ("arm64: mm: print out correct page table entries")
does, drop the struct mm_struct argument of show_pte(), print the tables
based on the faulting address.

Signed-off-by: Kefeng Wang <[e-mail]>
---
 arch/arm/include/asm/bug.h |  2 +-
 arch/arm/kernel/traps.c    |  2 +-
 arch/arm/mm/fault.c        | 36 ++++++++++++++++++++----------------
 3 files changed, 22 insertions(+), 18 deletions(-)

Comments

Russell King (Oracle) June 2, 2021, 10:44 a.m. UTC | #1

On Wed, Jun 02, 2021 at 03:02:43PM +0800, Kefeng Wang wrote:
> Like commit 67ce16ec15ce ("arm64: mm: print out correct page table entries")
> does, drop the struct mm_struct argument of show_pte(), print the tables
> based on the faulting address.
> 
> Signed-off-by: Kefeng Wang <[e-mail]>

This can be misleading on 32-bit ARM.

The effective page tables for each thread are the threads *own* page
tables. There is no hardware magic for addresses above PAGE_OFFSET being
directed to the init_mm page tables.

So, when we hit a fault in kernel space, we need to be printing the
currently in-use page tables associated with the running thread.

Hence:

>  /*
> - * This is useful to dump out the page tables associated with
> - * 'addr' in mm 'mm'.
> + * Dump out the page tables associated with 'addr' in the currently active mm
>   */
> -void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
> +void show_pte(const char *lvl, unsigned long addr)
>  {
>  	pgd_t *pgd;
> -
> -	if (!mm)
> +	struct mm_struct *mm;
> +
> +	if (addr < TASK_SIZE) {
> +		mm = current->active_mm;
> +		if (mm == &init_mm) {
> +			printk("%s[%08lx] user address but active_mm is swapper\n",
> +				lvl, addr);
> +			return;
> +		}
> +	} else {
>  		mm = &init_mm;
> +	}

is incorrect here.

It's completely fine for architectures where kernel accesses always go
to the init_mm page tables, but for 32-bit ARM that is not the case.

Kefeng Wang June 2, 2021, 11:24 a.m. UTC | #2

On 2021/6/2 18:44, Russell King (Oracle) wrote:
> On Wed, Jun 02, 2021 at 03:02:43PM +0800, Kefeng Wang wrote:
>> Like commit 67ce16ec15ce ("arm64: mm: print out correct page table entries")
>> does, drop the struct mm_struct argument of show_pte(), print the tables
>> based on the faulting address.
>>
>> Signed-off-by: Kefeng Wang <[e-mail]>
> This can be misleading on 32-bit ARM.
>
> The effective page tables for each thread are the threads *own* page
> tables. There is no hardware magic for addresses above PAGE_OFFSET being
> directed to the init_mm page tables.
>
> So, when we hit a fault in kernel space, we need to be printing the
> currently in-use page tables associated with the running thread.
>
> Hence:
>
>>   /*
>> - * This is useful to dump out the page tables associated with
>> - * 'addr' in mm 'mm'.
>> + * Dump out the page tables associated with 'addr' in the currently active mm
>>    */
>> -void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
>> +void show_pte(const char *lvl, unsigned long addr)
>>   {
>>   	pgd_t *pgd;
>> -
>> -	if (!mm)
>> +	struct mm_struct *mm;
>> +
>> +	if (addr < TASK_SIZE) {
>> +		mm = current->active_mm;
>> +		if (mm == &init_mm) {
>> +			printk("%s[%08lx] user address but active_mm is swapper\n",
>> +				lvl, addr);
>> +			return;
>> +		}
>> +	} else {
>>   		mm = &init_mm;
>> +	}
> is incorrect here.
>
> It's completely fine for architectures where kernel accesses always go
> to the init_mm page tables, but for 32-bit ARM that is not the case.
OK, I will drop this one, thanks
>

Patch

diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h
index ba8d9d7d242b..d618640e34aa 100644
--- a/arch/arm/include/asm/bug.h
+++ b/arch/arm/include/asm/bug.h
@@ -86,7 +86,7 @@  extern asmlinkage void c_backtrace(unsigned long fp, int pmode,
 				   const char *loglvl);
 
 struct mm_struct;
-void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr);
+void show_pte(const char *lvl, unsigned long addr);
 extern void __show_regs(struct pt_regs *);
 extern void __show_regs_alloc_free(struct pt_regs *regs);
 
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 64308e3a5d0c..98c904aeee78 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -736,7 +736,7 @@  baddataabort(int code, unsigned long instr, struct pt_regs *regs)
 		pr_err("[%d] %s: bad data abort: code %d instr 0x%08lx\n",
 		       task_pid_nr(current), current->comm, code, instr);
 		dump_instr(KERN_ERR, regs);
-		show_pte(KERN_ERR, current->mm, addr);
+		show_pte(KERN_ERR, addr);
 	}
 #endif
 
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 9a6d74f6ea1d..71a5c29488c2 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -27,15 +27,23 @@ 
 #ifdef CONFIG_MMU
 
 /*
- * This is useful to dump out the page tables associated with
- * 'addr' in mm 'mm'.
+ * Dump out the page tables associated with 'addr' in the currently active mm
  */
-void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
+void show_pte(const char *lvl, unsigned long addr)
 {
 	pgd_t *pgd;
-
-	if (!mm)
+	struct mm_struct *mm;
+
+	if (addr < TASK_SIZE) {
+		mm = current->active_mm;
+		if (mm == &init_mm) {
+			printk("%s[%08lx] user address but active_mm is swapper\n",
+				lvl, addr);
+			return;
+		}
+	} else {
 		mm = &init_mm;
+	}
 
 	printk("%spgd = %p\n", lvl, mm->pgd);
 	pgd = pgd_offset(mm, addr);
@@ -96,7 +104,7 @@  void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
 	pr_cont("\n");
 }
 #else					/* CONFIG_MMU */
-void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
+void show_pte(const char *lvl, unsigned long addr)
 { }
 #endif					/* CONFIG_MMU */
 
@@ -104,8 +112,7 @@  void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
  * Oops.  The kernel tried to access some page that wasn't present.
  */
 static void
-__do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
-		  struct pt_regs *regs)
+__do_kernel_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 {
 	/*
 	 * Are we prepared to handle this kernel fault?
@@ -122,7 +129,7 @@  __do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
 		 (addr < PAGE_SIZE) ? "NULL pointer dereference" :
 		 "paging request", addr);
 
-	show_pte(KERN_ALERT, mm, addr);
+	show_pte(KERN_ALERT, addr);
 	die("Oops", regs, fsr);
 	bust_spinlocks(0);
 	do_exit(SIGKILL);
@@ -147,7 +154,7 @@  __do_user_fault(unsigned long addr, unsigned int fsr, unsigned int sig,
 		pr_err("8<--- cut here ---\n");
 		pr_err("%s: unhandled page fault (%d) at 0x%08lx, code 0x%03x\n",
 		       tsk->comm, sig, addr, fsr);
-		show_pte(KERN_ERR, tsk->mm, addr);
+		show_pte(KERN_ERR, addr);
 		show_regs(regs);
 	}
 #endif
@@ -166,9 +173,6 @@  __do_user_fault(unsigned long addr, unsigned int fsr, unsigned int sig,
 
 void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 {
-	struct task_struct *tsk = current;
-	struct mm_struct *mm = tsk->active_mm;
-
 	/*
 	 * If we are in kernel mode at this point, we
 	 * have no context to handle this fault with.
@@ -176,7 +180,7 @@  void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	if (user_mode(regs))
 		__do_user_fault(addr, fsr, SIGSEGV, SEGV_MAPERR, regs);
 	else
-		__do_kernel_fault(mm, addr, fsr, regs);
+		__do_kernel_fault(addr, fsr, regs);
 }
 
 #ifdef CONFIG_MMU
@@ -336,7 +340,7 @@  do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	return 0;
 
 no_context:
-	__do_kernel_fault(mm, addr, fsr, regs);
+	__do_kernel_fault(addr, fsr, regs);
 	return 0;
 }
 #else					/* CONFIG_MMU */
@@ -503,7 +507,7 @@  do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	pr_alert("8<--- cut here ---\n");
 	pr_alert("Unhandled fault: %s (0x%03x) at 0x%08lx\n",
 		inf->name, fsr, addr);
-	show_pte(KERN_ALERT, current->mm, addr);
+	show_pte(KERN_ALERT, addr);
 
 	arm_notify_die("", regs, inf->sig, inf->code, (void __user *)addr,
 		       fsr, 0);