s390: add no-execute support
Bit 0x100 of a page table, segment table of region table entry
can be used to disallow code execution for the virtual addresses
associated with the entry.
There is one tricky bit, the system call to return from a signal
is part of the signal frame written to the user stack. With a
non-executable stack this would stop working. To avoid breaking
things the protection fault handler checks the opcode that caused
the fault for 0x0a77 (sys_sigreturn) and 0x0aad (sys_rt_sigreturn)
and injects a system call. This is preferable to the alternative
solution with a stub function in the vdso because it works for
vdso=off and statically linked binaries as well.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/include/asm/setup.h b/arch/s390/include/asm/setup.h
index 5e8d57e..040a4b4 100644
--- a/arch/s390/include/asm/setup.h
+++ b/arch/s390/include/asm/setup.h
@@ -30,6 +30,7 @@
#define MACHINE_FLAG_TLB_LC _BITUL(12)
#define MACHINE_FLAG_VX _BITUL(13)
#define MACHINE_FLAG_CAD _BITUL(14)
+#define MACHINE_FLAG_NX _BITUL(15)
#define LPP_MAGIC _BITUL(31)
#define LPP_PFAULT_PID_MASK _AC(0xffffffff, UL)
@@ -71,6 +72,7 @@ extern void detect_memory_memblock(void);
#define MACHINE_HAS_TLB_LC (S390_lowcore.machine_flags & MACHINE_FLAG_TLB_LC)
#define MACHINE_HAS_VX (S390_lowcore.machine_flags & MACHINE_FLAG_VX)
#define MACHINE_HAS_CAD (S390_lowcore.machine_flags & MACHINE_FLAG_CAD)
+#define MACHINE_HAS_NX (S390_lowcore.machine_flags & MACHINE_FLAG_NX)
/*
* Console mode. Override with conmode=