linux-kernel - Re: [RFC PATCH 08/10] powerpc/fsl_booke/kaslr: clear the original kernel if randomized

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Message-ID: <a09b4f53-2ccd-e675-4385-b53fd91fbafc@c-s.fr>
Date:   Mon, 29 Jul 2019 13:19:41 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Jason Yan <yanaijie@...wei.com>, mpe@...erman.id.au,
        linuxppc-dev@...ts.ozlabs.org, diana.craciun@....com,
        benh@...nel.crashing.org, paulus@...ba.org, npiggin@...il.com,
        keescook@...omium.org, kernel-hardening@...ts.openwall.com
Cc:     linux-kernel@...r.kernel.org, wangkefeng.wang@...wei.com,
        yebin10@...wei.com, thunder.leizhen@...wei.com,
        jingxiangfeng@...wei.com, fanchengyang@...wei.com
Subject: Re: [RFC PATCH 08/10] powerpc/fsl_booke/kaslr: clear the original
 kernel if randomized



Le 17/07/2019 à 10:06, Jason Yan a écrit :
> The original kernel still exists in the memory, clear it now.
> 
> Signed-off-by: Jason Yan <yanaijie@...wei.com>
> Cc: Diana Craciun <diana.craciun@....com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Christophe Leroy <christophe.leroy@....fr>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Kees Cook <keescook@...omium.org>
> ---
>   arch/powerpc/kernel/kaslr_booke.c  | 11 +++++++++++
>   arch/powerpc/mm/mmu_decl.h         |  2 ++
>   arch/powerpc/mm/nohash/fsl_booke.c |  1 +
>   3 files changed, 14 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/kaslr_booke.c b/arch/powerpc/kernel/kaslr_booke.c
> index 90357f4bd313..00339c05879f 100644
> --- a/arch/powerpc/kernel/kaslr_booke.c
> +++ b/arch/powerpc/kernel/kaslr_booke.c
> @@ -412,3 +412,14 @@ notrace void __init kaslr_early_init(void *dt_ptr, phys_addr_t size)
>   
>   	reloc_kernel_entry(dt_ptr, kimage_vaddr);
>   }
> +
> +void __init kaslr_second_init(void)
> +{
> +	/* If randomized, clear the original kernel */
> +	if (kimage_vaddr != KERNELBASE) {
> +		unsigned long kernel_sz;
> +
> +		kernel_sz = (unsigned long)_end - kimage_vaddr;
> +		memset((void *)KERNELBASE, 0, kernel_sz);

Why are we clearing ? Is that just to tidy up or is it of security 
importance ?

If so, maybe memzero_explicit() should be used instead ?

> +	}
> +}
> diff --git a/arch/powerpc/mm/mmu_decl.h b/arch/powerpc/mm/mmu_decl.h
> index 754ae1e69f92..9912ee598f9b 100644
> --- a/arch/powerpc/mm/mmu_decl.h
> +++ b/arch/powerpc/mm/mmu_decl.h
> @@ -150,8 +150,10 @@ extern void loadcam_multi(int first_idx, int num, int tmp_idx);
>   
>   #ifdef CONFIG_RANDOMIZE_BASE
>   extern void kaslr_early_init(void *dt_ptr, phys_addr_t size);
> +extern void kaslr_second_init(void);

No new 'extern' please.

>   #else
>   static inline void kaslr_early_init(void *dt_ptr, phys_addr_t size) {}
> +static inline void kaslr_second_init(void) {}
>   #endif
>   
>   struct tlbcam {
> diff --git a/arch/powerpc/mm/nohash/fsl_booke.c b/arch/powerpc/mm/nohash/fsl_booke.c
> index 8d25a8dc965f..fa5a87f5c08e 100644
> --- a/arch/powerpc/mm/nohash/fsl_booke.c
> +++ b/arch/powerpc/mm/nohash/fsl_booke.c
> @@ -269,6 +269,7 @@ notrace void __init relocate_init(u64 dt_ptr, phys_addr_t start)
>   	kernstart_addr = start;
>   	if (is_second_reloc) {
>   		virt_phys_offset = PAGE_OFFSET - memstart_addr;
> +		kaslr_second_init();
>   		return;
>   	}
>   
> 

Christophe