linux-kernel - Re: [PATCH V2] mips: kernel: fix detect_memory

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Date: Tue, 25 Jun 2024 02:58:54 +0100
From: "Jiaxun Yang" <jiaxun.yang@...goat.com>
To: "Shiji Yang" <yangshiji66@...look.com>,
 "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>
Cc: "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 "Arnd Bergmann" <arnd@...db.de>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
 "Javier Martinez Canillas" <javierm@...hat.com>,
 "Khalid Aziz" <khalid@...ehiking.org>, "Baoquan He" <bhe@...hat.com>,
 "Serge Semin" <fancer.lancer@...il.com>, linux-kernel@...r.kernel.org,
 "Mieczyslaw Nalewaj" <namiltd@...oo.com>
Subject: Re: [PATCH V2] mips: kernel: fix detect_memory_region() function



在2024年6月25日六月 上午2:44，Shiji Yang写道：
> The detect_memory_region() has been broken on 6.6 kernel[1]. This
> patch fixes it by:
> 1. Do not use memcmp() on unallocated memory, as the new introduced
>    fortify dynamic object size check[2] will return unexpected result.
> 2. Use a fixed pattern instead of a random function pointer as the
>    magic value.
> 3. Flip magic value and double check it.
> 4. Enable this feature only for 32-bit CPUs. Currently, only ath79 and
>    ralink CPUs are using it. And 64-bit CPU doesn't have the KSEG1ADDR
>    definition.

Hi Shiji,

Thanks for your patch.

Please don't break 64bit system.
Use CKSEG1ADDR_OR_64BIT instead.

Thanks
- Jiaxun

>
> [1] 
> https://github.com/openwrt/openwrt/pull/14774#issuecomment-1989356746
> [2] commit 439a1bcac648 ("fortify: Use __builtin_dynamic_object_size() 
> when available")
> Signed-off-by: Shiji Yang <yangshiji66@...look.com>
> Tested-by: Mieczyslaw Nalewaj <namiltd@...oo.com>
> ---
>  arch/mips/include/asm/bootinfo.h |  2 ++
>  arch/mips/kernel/setup.c         | 17 ++++++++++++-----
>  2 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/arch/mips/include/asm/bootinfo.h b/arch/mips/include/asm/bootinfo.h
> index 2128ba903391..8516c11916a4 100644
> --- a/arch/mips/include/asm/bootinfo.h
> +++ b/arch/mips/include/asm/bootinfo.h
> @@ -93,7 +93,9 @@ const char *get_system_type(void);
> 
>  extern unsigned long mips_machtype;
> 
> +#ifndef CONFIG_64BIT
>  extern void detect_memory_region(phys_addr_t start, phys_addr_t 
> sz_min,  phys_addr_t sz_max);
> +#endif
> 
>  extern void prom_init(void);
>  extern void prom_free_prom_memory(void);
> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> index 12a1a4ffb602..3a3bc1b7e62e 100644
> --- a/arch/mips/kernel/setup.c
> +++ b/arch/mips/kernel/setup.c
> @@ -86,21 +86,27 @@ static struct resource bss_resource = { .name = 
> "Kernel bss", };
>  unsigned long __kaslr_offset __ro_after_init;
>  EXPORT_SYMBOL(__kaslr_offset);
> 
> -static void *detect_magic __initdata = detect_memory_region;
> -
>  #ifdef CONFIG_MIPS_AUTO_PFN_OFFSET
>  unsigned long ARCH_PFN_OFFSET;
>  EXPORT_SYMBOL(ARCH_PFN_OFFSET);
>  #endif
> 
> +#ifndef CONFIG_64BIT
> +static u32 detect_magic __initdata;
> +#define MIPS_MEM_TEST_PATTERN		0xaa5555aa
> +
>  void __init detect_memory_region(phys_addr_t start, phys_addr_t 
> sz_min, phys_addr_t sz_max)
>  {
> -	void *dm = &detect_magic;
> +	void *dm = (void *)KSEG1ADDR(&detect_magic);
>  	phys_addr_t size;
> 
>  	for (size = sz_min; size < sz_max; size <<= 1) {
> -		if (!memcmp(dm, dm + size, sizeof(detect_magic)))
> -			break;
> +		__raw_writel(MIPS_MEM_TEST_PATTERN, dm);
> +		if (__raw_readl(dm) == __raw_readl(dm + size)) {
> +			__raw_writel(~MIPS_MEM_TEST_PATTERN, dm);
> +			if (__raw_readl(dm) == __raw_readl(dm + size))
> +				break;
> +		}
>  	}
> 
>  	pr_debug("Memory: %lluMB of RAM detected at 0x%llx (min: %lluMB, max: 
> %lluMB)\n",
> @@ -111,6 +117,7 @@ void __init detect_memory_region(phys_addr_t start, 
> phys_addr_t sz_min, phys_add
> 
>  	memblock_add(start, size);
>  }
> +#endif /* CONFIG_64BIT */
> 
>  /*
>   * Manage initrd
> -- 
> 2.45.1

-- 
- Jiaxun