[PATCH] arm64: print a fault message when attempting to write RO memory

From: Stephen Boyd
Date: Wed Feb 15 2017 - 20:55:20 EST

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:

Internal error: Attempting to write read-only memory: 9600004f [#1] PREEMPT SMP

Cc: Laura Abbott <labbott@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Stephen Boyd <stephen.boyd@xxxxxxxxxx>
arch/arm64/mm/fault.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 156169c6981b..752507fa80ec 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -331,6 +331,11 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,

if (!search_exception_tables(regs->pc))
die("Accessing user space memory outside uaccess.h routines", regs, esr);
+ } else if (is_permission_fault(esr, regs)) {
+ if (esr & ESR_ELx_WNR)
+ die("Attempting to write read-only memory", regs, esr);
+ else
+ die("Attempting to read unreadable memory", regs, esr);