linux-kernel - Re: [PATCH v2 07/10] powerpc/fsl_booke/32: randomize the kernel image offset

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Message-ID: <ab36084e-6cce-89d6-52a7-5c5fe06642b8@huawei.com>
Date:   Wed, 31 Jul 2019 10:06:55 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     Christophe Leroy <christophe.leroy@....fr>, <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>,
        <zhaohongjiang@...wei.com>
Subject: Re: [PATCH v2 07/10] powerpc/fsl_booke/32: randomize the kernel image
 offset



On 2019/7/30 17:44, Christophe Leroy wrote:
> 
> 
> Le 30/07/2019 à 09:42, Jason Yan a écrit :
>> After we have the basic support of relocate the kernel in some
>> appropriate place, we can start to randomize the offset now.
>>
>> Entropy is derived from the banner and timer, which will change every
>> build and boot. This not so much safe so additionally the bootloader may
>> pass entropy via the /chosen/kaslr-seed node in device tree.
>>
>> We will use the first 512M of the low memory to randomize the kernel
>> image. The memory will be split in 64M zones. We will use the lower 8
>> bit of the entropy to decide the index of the 64M zone. Then we chose a
>> 16K aligned offset inside the 64M zone to put the kernel in.
>>
>>      KERNELBASE
>>
>>          |-->   64M   <--|
>>          |               |
>>          +---------------+    +----------------+---------------+
>>          |               |....|    |kernel|    |               |
>>          +---------------+    +----------------+---------------+
>>          |                         |
>>          |----->   offset    <-----|
>>
>>                                kimage_vaddr
>>
>> We also check if we will overlap with some areas like the dtb area, the
>> initrd area or the crashkernel area. If we cannot find a proper area,
>> kaslr will be disabled and boot from the original kernel.
>>
>> 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 | 334 +++++++++++++++++++++++++++++-
>>   1 file changed, 332 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/kaslr_booke.c 
>> b/arch/powerpc/kernel/kaslr_booke.c
>> index 960bce4aa8b9..0bb02e45b928 100644
>> --- a/arch/powerpc/kernel/kaslr_booke.c
>> +++ b/arch/powerpc/kernel/kaslr_booke.c
>> @@ -23,6 +23,8 @@
>>   #include <linux/delay.h>
>>   #include <linux/highmem.h>
>>   #include <linux/memblock.h>
>> +#include <linux/libfdt.h>
>> +#include <linux/crash_core.h>
>>   #include <asm/pgalloc.h>
>>   #include <asm/prom.h>
>>   #include <asm/io.h>
>> @@ -34,15 +36,341 @@
>>   #include <asm/machdep.h>
>>   #include <asm/setup.h>
>>   #include <asm/paca.h>
>> +#include <asm/kdump.h>
>>   #include <mm/mmu_decl.h>
>> +#include <generated/compile.h>
>> +#include <generated/utsrelease.h>
>> +
>> +#ifdef DEBUG
>> +#define DBG(fmt...) printk(KERN_ERR fmt)
>> +#else
>> +#define DBG(fmt...)
>> +#endif
>> +
>> +struct regions {
>> +    unsigned long pa_start;
>> +    unsigned long pa_end;
>> +    unsigned long kernel_size;
>> +    unsigned long dtb_start;
>> +    unsigned long dtb_end;
>> +    unsigned long initrd_start;
>> +    unsigned long initrd_end;
>> +    unsigned long crash_start;
>> +    unsigned long crash_end;
>> +    int reserved_mem;
>> +    int reserved_mem_addr_cells;
>> +    int reserved_mem_size_cells;
>> +};
>>   extern int is_second_reloc;
>> +/* Simplified build-specific string for starting entropy. */
>> +static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
>> +        LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
>> +
>> +static __init void kaslr_get_cmdline(void *fdt)
>> +{
>> +    const char *cmdline = CONFIG_CMDLINE;
>> +    if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
>> +        int node;
>> +        const u8 *prop;
>> +        node = fdt_path_offset(fdt, "/chosen");
>> +        if (node < 0)
>> +            goto out;
>> +
>> +        prop = fdt_getprop(fdt, node, "bootargs", NULL);
>> +        if (!prop)
>> +            goto out;
>> +        cmdline = prop;
>> +    }
>> +out:
>> +    strscpy(boot_command_line, cmdline, COMMAND_LINE_SIZE);
> 
> boot_command_line is set by early_init_devtree() in 
> arch/powerpc/kernel/prom.c
> Is that too late for you ?
> 

Yes, it's too late.

> If so, what about calling early_init_dt_scan_chosen() instead of recoding ?
> 

Good suggestion. I will have a try.

> Christophe
> 
> .
>