From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 734B71A03D6 for ; Wed, 11 Feb 2015 13:57:44 +1100 (AEDT) Message-ID: <1423620717.5891.31.camel@kernel.crashing.org> Subject: Re: [PATCH 3/4] powerpc/boot: Fix stack corruption in epapr entry point From: Benjamin Herrenschmidt To: Jeremy Kerr Date: Wed, 11 Feb 2015 13:11:57 +1100 In-Reply-To: <1423570510.219047.52227904007.3.gpush@pablo> References: <1423570510.219047.52227904007.3.gpush@pablo> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 2015-02-10 at 20:15 +0800, Jeremy Kerr wrote: > Currently, a 64-bit little-endian zImage.epapr won't boot in epapr mode, > as as we never return from platform_init. > > Before entering C, we initialise our stack by setting r1 16 bytes below > the end of the _bss_stack: > > stwu r0,-16(r1) /* establish a stack frame */ > > However, the called function will save the caller's lr in the caller's > frame's lr save area, at -16(r1) to -32(r1). > > This means that writes to the fdt variable corrupt the saved link > register: > > 0000000020c06018 l O .bss 0000000000001000 _bss_stack > 0000000020c07018 l O .bss 0000000000000008 fdt > > This change allocates the minimum of 32 bytes for the base of the stack > instead. Is that sufficient for ABI v1 ? It feels like it's broken for BE as well... Ben. > Signed-off-by: Jeremy Kerr > > --- > arch/powerpc/boot/crt0.S | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/powerpc/boot/crt0.S b/arch/powerpc/boot/crt0.S > index 14de4f8..bf8eeee 100644 > --- a/arch/powerpc/boot/crt0.S > +++ b/arch/powerpc/boot/crt0.S > @@ -218,7 +218,7 @@ p_base: mflr r10 /* r10 now points to runtime addr of p_base */ > beq 6f > ld r1,0(r8) > li r0,0 > - stdu r0,-16(r1) /* establish a stack frame */ > + stdu r0,-32(r1) /* establish a stack frame */ > 6: > #endif /* __powerpc64__ */ > /* Call platform_init() */ > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev@lists.ozlabs.org > https://lists.ozlabs.org/listinfo/linuxppc-dev