Patch "powerpc: Add missing error check to prom_find_boot_cpu()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

powerpc: Add missing error check to prom_find_boot_cpu()

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-add-missing-error-check-to-prom_find_boot_cpu.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Darren Stevens <[email protected]>
Date: Mon, 23 Jan 2017 19:42:54 +0000
Subject: powerpc: Add missing error check to prom_find_boot_cpu()

From: Darren Stevens <[email protected]>

commit af2b7fa17eb92e52b65f96604448ff7a2a89ee99 upstream.

prom_init.c calls 'instance-to-package' twice, but the return is not checked during prom_find_boot_cpu(). The result is then passed to prom_getprop(), which could be PROM_ERROR. Add a return check to prevent this.

This was found on a pasemi system, where CFE doesn't have a working 'instance-to package' prom call.

Before Commit 5c0484e25ec0 ('powerpc: Endian safe trampoline') the area around addr 0 was mostly 0's and this doesn't cause a problem. Once the macro 'FIXUP_ENDIAN' has been added to head_64.S, the low memory area now has non-zero values, which cause the prom_getprop() call to hang.

mpe: Also confirmed that under SLOF if 'instance-to-package' did fail with PROM_ERROR we would crash in SLOF. So the bug is not specific to CFE, it's just that other open firmwares don't trigger it because they have a working 'instance-to-package'.

---
 arch/powerpc/kernel/prom_init.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -2747,6 +2747,9 @@ static void __init prom_find_boot_cpu(vo
 
 	cpu_pkg = call_prom("instance-to-package", 1, 1, prom_cpu);
 
+	if (!PHANDLE_VALID(cpu_pkg))
+		return;
+
 	prom_getprop(cpu_pkg, "reg", &rval, sizeof(rval));
 	prom.cpu = be32_to_cpu(rval);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/powerpc-add-missing-error-check-to-prom_find_boot_cpu.patch