FAILED: patch "[PATCH] powerpc/mm/radix: Only add X for pages overlapping kernel" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Michael Ellerman <[email protected]>
Date: Tue, 6 Jun 2017 15:48:57 +1000
Subject: [PATCH] powerpc/mm/radix: Only add X for pages overlapping kernel
text

Currently we map the whole linear mapping with PAGE_KERNEL_X. Instead we should check if the page overlaps the kernel text and only then add PAGE_KERNEL_X.

Note that we still use 1G pages if they're available, so this will typically still result in a 1G executable page at KERNELBASE. So this fix is primarily useful for catching stray branches to high linear mapping addresses.

Without this patch, we can execute at 1G in xmon using:

0:mon> m c000000040000000

  c000000040000000  00 l
  c000000040000000  00000000 01006038
  c000000040000004  00000000 2000804e
  c000000040000008  00000000 x
  0:mon> di c000000040000000
  c000000040000000  38600001      li      r3,1
  c000000040000004  4e800020      blr

0:mon> p c000000040000000
return value is 0x1

After we get a 400 as expected:

0:mon> p c000000040000000
*** 400 exception occurred

index c28165d8970b..6c062f92b9e4 100644
@@ -19,6 +19,7 @@
 #include <asm/mmu.h>
 #include <asm/firmware.h>
 #include <asm/powernv.h>
+#include <asm/sections.h>
 
 #include <trace/events/thp.h>
 

@@ -121,7 +122,8 @@ static inline void __meminit print_mapping(unsigned long start,
 static int __meminit create_physical_mapping(unsigned long start,
 					     unsigned long end)
 {
-	unsigned long addr, mapping_size = 0;
+	unsigned long vaddr, addr, mapping_size = 0;
+	pgprot_t prot;
 
 	start = _ALIGN_UP(start, PAGE_SIZE);
 	for (addr = start; addr < end; addr += mapping_size) {

@@ -145,8 +147,14 @@ static int __meminit create_physical_mapping(unsigned long start,
 			start = addr;
 		}
 
-		rc = radix__map_kernel_page((unsigned long)__va(addr), addr,
-					    PAGE_KERNEL_X, mapping_size);
+		vaddr = (unsigned long)__va(addr);
+
+		if (overlaps_kernel_text(vaddr, vaddr + mapping_size))
+			prot = PAGE_KERNEL_X;
+		else
+			prot = PAGE_KERNEL;
+
+		rc = radix__map_kernel_page(vaddr, addr, prot, mapping_size);
 		if (rc)
 			return rc;
 	}