[PATCH] powerpc/64: Fix booting large kernels with STRICT_KERNEL_RWX

[PATCH] powerpc/64: Fix booting large kernels with STRICT_KERNEL_RWX

[Russell Currey]

With STRICT_KERNEL_RWX enabled anything marked __init is placed at a 16M
boundary.  This is necessary so that it can be repurposed later with
different permissions.  However, in kernels with text larger than 16M,
this pushes early_setup past 32M, incapable of being reached by the
branch instruction.

Fix this by setting the CTR and branching there instead.

Fixes: 1e0fc9d1eb2b ("powerpc/Kconfig: Enable STRICT_KERNEL_RWX for some configs")
Signed-off-by: Russell Currey <ruscur@russell.cc>
---
 arch/powerpc/kernel/head_64.S | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 3fad8d499767..c2b53febadd9 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -968,7 +968,9 @@ start_here_multiplatform:
 
 	/* Restore parameters passed from prom_init/kexec */
 	mr	r3,r31
-	bl	early_setup		/* also sets r13 and SPRG_PACA */
+	LOAD_REG_ADDR(r12, early_setup)
+	mtctr	r12
+	bctrl		/* also sets r13 and SPRG_PACA */
 
 	LOAD_REG_ADDR(r3, start_here_common)
 	ld	r4,PACAKMSR(r13)
-- 
2.21.0

Re: powerpc/64: Fix booting large kernels with STRICT_KERNEL_RWX

[Michael Ellerman]

On Wed, 2019-03-27 at 03:35:54 UTC, Russell Currey wrote:
> With STRICT_KERNEL_RWX enabled anything marked __init is placed at a 16M
> boundary.  This is necessary so that it can be repurposed later with
> different permissions.  However, in kernels with text larger than 16M,
> this pushes early_setup past 32M, incapable of being reached by the
> branch instruction.
> 
> Fix this by setting the CTR and branching there instead.
> 
> Fixes: 1e0fc9d1eb2b ("powerpc/Kconfig: Enable STRICT_KERNEL_RWX for some configs")
> Signed-off-by: Russell Currey <ruscur@russell.cc>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/56c46bba9bbfe229b4472a5be313c44c

cheers