A protection key fault is very similar to any other access
error. There must be a VMA, etc... We even want to take
the same action (SIGSEGV) that we do with a normal access
fault.
However, we do need to let userspace know that something
is different. We do this the same way what we did with
SEGV_BNDERR with Memory Protection eXtensions (MPX):
define a new SEGV code: SEGV_PKUERR.
We will, at some point need to allow userspace a way to
figure out which protection key coveres the address that
we faulted on. We can either do that with a separate
interface, or we could pass it up in the siginfo like
MPX did.
Suggestions welcome. :)
---
b/arch/x86/mm/fault.c | 5 ++++-
b/include/uapi/asm-generic/siginfo.h | 10 +++++++++-
2 files changed, 13 insertions(+), 2 deletions(-)
diff -puN arch/x86/mm/fault.c~pkeys-13-siginfo arch/x86/mm/fault.c
--- a/arch/x86/mm/fault.c~pkeys-13-siginfo 2015-05-07 10:31:44.169312893
-0700
+++ b/arch/x86/mm/fault.c 2015-05-07 10:31:44.174313118 -0700
@@ -838,7 +838,10 @@ static noinline void
bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
unsigned long address)
{
- __bad_area(regs, error_code, address, SEGV_ACCERR);
+ if (error_code & PF_PK)
+ __bad_area(regs, error_code, address, SEGV_PKUERR);
+ else
+ __bad_area(regs, error_code, address, SEGV_ACCERR);
}
static void
diff -puN include/uapi/asm-generic/siginfo.h~pkeys-13-siginfo
include/uapi/asm-generic/siginfo.h
--- a/include/uapi/asm-generic/siginfo.h~pkeys-13-siginfo 2015-05-07
10:31:44.170312938 -0700
+++ b/include/uapi/asm-generic/siginfo.h 2015-05-07 10:31:44.174313118
-0700
@@ -95,6 +95,13 @@ typedef struct siginfo {
void __user *_lower;
void __user *_upper;
} _addr_bnd;
+ int protection_key; /* FIXME: protection key value??
+ * Do we really need this in here?
+ * userspace can get the PKRU value
in
+ * the signal handler, but they do
not
+ * easily have access to the PKEY
value
+ * from the PTE.
+ */
} _sigfault;
/* SIGPOLL */
@@ -206,7 +213,8 @@ typedef struct siginfo {
#define SEGV_MAPERR (__SI_FAULT|1) /* address not mapped to object */
#define SEGV_ACCERR (__SI_FAULT|2) /* invalid permissions for mapped
object */
#define SEGV_BNDERR (__SI_FAULT|3) /* failed address bound checks */
-#define NSIGSEGV 3
+#define SEGV_PKUERR (__SI_FAULT|4) /* failed address bound checks */
+#define NSIGSEGV 4
/*
* SIGBUS si_codes
_
--
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