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: James Morse <[email protected]>
Tested-by: James Morse <[email protected]>
Acked-by: Laura Abbott <[email protected]>
Cc: Mark Rutland <[email protected]>
Signed-off-by: Stephen Boyd <[email protected]>
---
Changes from v3:
* Don't drop addr check in do_page_fault() (James Morse)
Changes from v2:
* Fold addr check into is_permission_fault() (James Morse)
Changes from v1:
* Move into __do_kernel_fault() (Mark Rutland)
arch/arm64/mm/fault.c | 55 +++++++++++++++++++++++++++++++++------------------
1 file changed, 36 insertions(+), 19 deletions(-)
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 156169c6981b..3bde99769679 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -160,12 +160,33 @@ 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.
@@ -177,9 +198,20 @@ 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);
@@ -269,21 +301,6 @@ 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;
@@ -321,7 +338,7 @@ 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);
--
2.10.0.297.gf6727b0
On Wed, Apr 05, 2017 at 12:18:31PM -0700, Stephen Boyd wrote:
> 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: James Morse <[email protected]>
> Tested-by: James Morse <[email protected]>
> Acked-by: Laura Abbott <[email protected]>
> Cc: Mark Rutland <[email protected]>
> Signed-off-by: Stephen Boyd <[email protected]>
Queued for 4.12. Thanks.
--
Catalin