ARM: kexec: Make .text R/W in machine_kexec

Remove DEBUG_RODATA dependence on !kexec since "ARM: kexec: Make .text R/W in machine_kexec" fixes the incompatibility between those 2
options.

Signed-off-by Nikolay Borisov <[email protected]>

Quoted 5 lines · Nikolay Borisov

Remove DEBUG_RODATA dependence on !kexec since "ARM: kexec: Make .text R/W in machine_kexec" fixes the incompatibility between those 2
options.

Signed-off-by Nikolay Borisov <[email protected]>

Acked-by Will Deacon <[email protected]>

Quoted 7 lines · Will Deacon

Quoted 5 lines · Nikolay Borisov

Remove DEBUG_RODATA dependence on !kexec since "ARM: kexec: Make .text R/W in machine_kexec" fixes the incompatibility between those 2
options.

Signed-off-by Nikolay Borisov <[email protected]>

Quoted 1 line

Acked-by Will Deacon <[email protected]>

We've got, from what I can see, about 4 sets of patches that are or revolve around DEBUG_RODATA. What do you think is the best way to gather everything together? Do you want me to build 1 giant set of patches that includes kexec, DEBUG_RODATA, FIXMAP, and kgdb all together, or should we just start flushing each one separately into the patch tracker?

Quoted 8 lines · Kees Cook

Quoted 7 lines · Will Deacon

Quoted 5 lines · Nikolay Borisov

Remove DEBUG_RODATA dependence on !kexec since "ARM: kexec: Make .text R/W in machine_kexec" fixes the incompatibility between those 2
options.

Signed-off-by Nikolay Borisov <[email protected]>

Quoted 8 lines

Quoted 1 line

Acked-by Will Deacon <[email protected]>

We've got, from what I can see, about 4 sets of patches that are or revolve around DEBUG_RODATA. What do you think is the best way to gather everything together? Do you want me to build 1 giant set of patches that includes kexec, DEBUG_RODATA, FIXMAP, and kgdb all together, or should we just start flushing each one separately into the patch tracker?

It's probably worth you collating the patches together into a single series, giving it some testing, then reposting that to the list. Then, assuming nothing explodes, sending a pull request to rmk (although it's getting quite late in the day for 3.16).

Sound like a plan?

With the introduction of Kees Cook's patch to make the kernel .text read-only the existing method by which kexec works got broken since it directly pokes some values in the template code, which resides in the .text section.

The current patch changes the way those values are inserted so that poking .text section occurs only in machine_kexec (e.g when we are about to nuke the old kernel and are beyond the point of return). This allows to use set_kernel_text_rw() to directly patch the values in the .text section.

I had already sent a patch which achieved this but it was significantly more complicated, so this is a cleaner/straight-forward approach.

Tested on 3.15-rc4

Signed-off-by Nikolay Borisov <[email protected]>

---
 arch/arm/kernel/machine_kexec.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

arch/arm/kernel/machine_kexec.c +2 -1

index 8cf0996..cee44db 100644
@@ -29,6 +29,7 @@ extern unsigned long kexec_boot_atags;
 
 static atomic_t waiting_for_crash_ipi;
 
+static unsigned long dt_mem;
 /*
  * Provide a dummy crash_notes definition while crash dump arrives to arm.
  * This prevents breakage of crash_notes attribute in kernel/ksysfs.c.

@@ -64,7 +65,7 @@ int machine_kexec_prepare(struct kimage *image)
 			return err;
 
 		if (be32_to_cpu(header) == OF_DT_HEADER)
-			kexec_boot_atags = current_segment->mem;
+			dt_mem = current_segment->mem;
 	}
 	return 0;
 }