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SubjectRe: [RFC PATCH 08/10] powerpc/fsl_booke/kaslr: clear the original kernel if randomized
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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@huawei.com>
> Cc: Diana Craciun <diana.craciun@nxp.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Christophe Leroy <christophe.leroy@c-s.fr>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Kees Cook <keescook@chromium.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

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