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Commit b824b930 authored by Stephen Boyd's avatar Stephen Boyd Committed by Catalin Marinas
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arm64: print a fault message when attempting to write RO memory 



If a page is marked read only we should print out that fact,
instead of printing out that there was a page fault. Right now we
get a cryptic error message that something went wrong with an
unhandled fault, but we don't evaluate the esr to figure out that
it was a read/write permission fault.

Instead of seeing:

  Unable to handle kernel paging request at virtual address ffff000008e460d8
  pgd = ffff800003504000
  [ffff000008e460d8] *pgd=0000000083473003, *pud=0000000083503003, *pmd=0000000000000000
  Internal error: Oops: 9600004f [#1] PREEMPT SMP

we'll see:

  Unable to handle kernel write to read-only memory at virtual address ffff000008e760d8
  pgd = ffff80003d3de000
  [ffff000008e760d8] *pgd=0000000083472003, *pud=0000000083435003, *pmd=0000000000000000
  Internal error: Oops: 9600004f [#1] PREEMPT SMP

We also add a userspace address check into is_permission_fault()
so that the function doesn't return true for ttbr0 PAN faults
when it shouldn't.

Reviewed-by: default avatarJames Morse <james.morse@arm.com>
Tested-by: default avatarJames Morse <james.morse@arm.com>
Acked-by: default avatarLaura Abbott <labbott@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarStephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent ae8a442d

arch/arm64/mm/fault.c

+36 −19
Original line number Diff line number Diff line
@@ -161,12 +161,33 @@ static bool is_el1_instruction_abort(unsigned int esr) 
	return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_CUR;

}



static inline bool is_permission_fault(unsigned int esr, struct pt_regs *regs,

				       unsigned long addr)

{

	unsigned int ec       = ESR_ELx_EC(esr);

	unsigned int fsc_type = esr & ESR_ELx_FSC_TYPE;



	if (ec != ESR_ELx_EC_DABT_CUR && ec != ESR_ELx_EC_IABT_CUR)

		return false;



	if (fsc_type == ESR_ELx_FSC_PERM)

		return true;



	if (addr < USER_DS && system_uses_ttbr0_pan())

		return fsc_type == ESR_ELx_FSC_FAULT &&

			(regs->pstate & PSR_PAN_BIT);



	return false;

}



/*

 * 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 esr, struct pt_regs *regs)

{

	const char *msg;



	/*

	 * Are we prepared to handle this kernel fault?

	 * We are almost certainly not prepared to handle instruction faults.
@@ -178,9 +199,20 @@ static void __do_kernel_fault(struct mm_struct *mm, unsigned long addr, 
	 * No handler, we'll have to terminate things with extreme prejudice.

	 */

	bust_spinlocks(1);

	pr_alert("Unable to handle kernel %s at virtual address %08lx\n",

		 (addr < PAGE_SIZE) ? "NULL pointer dereference" :

		 "paging request", addr);



	if (is_permission_fault(esr, regs, addr)) {

		if (esr & ESR_ELx_WNR)

			msg = "write to read-only memory";

		else

			msg = "read from unreadable memory";

	} else if (addr < PAGE_SIZE) {

		msg = "NULL pointer dereference";

	} else {

		msg = "paging request";

	}



	pr_alert("Unable to handle kernel %s at virtual address %08lx\n", msg,

		 addr);



	show_pte(mm, addr);

	die("Oops", regs, esr);
@@ -270,21 +302,6 @@ static int __do_page_fault(struct mm_struct *mm, unsigned long addr, 
	return fault;

}



static inline bool is_permission_fault(unsigned int esr, struct pt_regs *regs)

{

	unsigned int ec       = ESR_ELx_EC(esr);

	unsigned int fsc_type = esr & ESR_ELx_FSC_TYPE;



	if (ec != ESR_ELx_EC_DABT_CUR && ec != ESR_ELx_EC_IABT_CUR)

		return false;



	if (system_uses_ttbr0_pan())

		return fsc_type == ESR_ELx_FSC_FAULT &&

			(regs->pstate & PSR_PAN_BIT);

	else

		return fsc_type == ESR_ELx_FSC_PERM;

}



static bool is_el0_instruction_abort(unsigned int esr)

{

	return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_LOW;
@@ -322,7 +339,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, 
		mm_flags |= FAULT_FLAG_WRITE;

	}



	if (addr < USER_DS && is_permission_fault(esr, regs)) {

	if (addr < USER_DS && is_permission_fault(esr, regs, addr)) {

		/* regs->orig_addr_limit may be 0 if we entered from EL0 */

		if (regs->orig_addr_limit == KERNEL_DS)

			die("Accessing user space memory with fs=KERNEL_DS", regs, esr);