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 Cc: James Morse <[email protected]> Cc: Laura Abbott <[email protected]> Cc: Mark Rutland <[email protected]> Signed-off-by: Stephen Boyd <[email protected]> --- Changes from v1: * Move into __do_kernel_fault() (Mark Rutland) arch/arm64/mm/fault.c | 47 +++++++++++++++++++++++++++++------------------ 1 file changed, 29 insertions(+), 18 deletions(-) diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 156169c6981b..8bd4e7f11c70 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -160,12 +160,28 @@ 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 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; +} + /* * 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. @@ -177,9 +193,19 @@ 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)) { + 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); @@ -269,21 +295,6 @@ 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; -- 2.10.0.297.gf6727b0
