linux-kernel - Re: [PATCH] parisc: Fix mmap_base calculation when stack grows upwards

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Message-ID: <ec0ef169-17b0-4dea-9378-7af8bae0662b@gmx.de>
Date:   Sun, 19 Nov 2023 16:20:09 +0100
From:   Helge Deller <deller@....de>
To:     Sam James <sam@...too.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org,
        matoro <matoro_mailinglist_kernel@...oro.tk>
Subject: Re: [PATCH] parisc: Fix mmap_base calculation when stack grows
 upwards

On 11/19/23 15:30, Sam James wrote:
>
> Helge Deller <deller@....de> writes:
>
>> Matoro reported various userspace crashes on the parisc platform with kernel
>> 6.6 and bisected it to commit 3033cd430768 ("parisc: Use generic mmap top-down
>> layout and brk randomization").
>>
>> That commit switched parisc to use the common infrastructure to calculate
>> mmap_base, but missed that the mmap_base() function takes care for
>> architectures where the stack grows downwards only.
>>
>> Fix the mmap_base() calculation to include the stack-grows-upwards case
>> and thus fix the userspace crashes on parisc.
>>
>> Reported-by: matoro <matoro_mailinglist_kernel@...oro.tk>
>> Signed-off-by: Helge Deller <deller@....de>
>> Tested-by: matoro <matoro_mailinglist_kernel@...oro.tk>
>> Fixes: 3033cd430768 ("parisc: Use generic mmap top-down layout and brk randomization")
>> Cc:  <stable@...r.kernel.org> # v6.6+
>
> Sorry to be impatient, but pinging this. HPPA is unusable on 6.6.x without this patch.

This patch was merged yesterday into Linus's master tree.
Now we just have to wait until it reaches the v6.6 stable tree...

Helge


>>
>> diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
>> index fd69dfa0cdab..a7c9c0e69e5a 100644
>> --- a/arch/parisc/Kconfig
>> +++ b/arch/parisc/Kconfig
>> @@ -140,11 +140,11 @@ config ARCH_MMAP_RND_COMPAT_BITS_MIN
>>   	default 8
>>
>>   config ARCH_MMAP_RND_BITS_MAX
>> -	default 24 if 64BIT
>> -	default 17
>> +	default 18 if 64BIT
>> +	default 13
>>
>>   config ARCH_MMAP_RND_COMPAT_BITS_MAX
>> -	default 17
>> +	default 13
>>
>>   # unless you want to implement ACPI on PA-RISC ... ;-)
>>   config PM
>> diff --git a/arch/parisc/include/asm/elf.h b/arch/parisc/include/asm/elf.h
>> index 140eaa97bf21..2d73d3c3cd37 100644
>> --- a/arch/parisc/include/asm/elf.h
>> +++ b/arch/parisc/include/asm/elf.h
>> @@ -349,15 +349,7 @@ struct pt_regs;	/* forward declaration... */
>>
>>   #define ELF_HWCAP	0
>>
>> -/* Masks for stack and mmap randomization */
>> -#define BRK_RND_MASK	(is_32bit_task() ? 0x07ffUL : 0x3ffffUL)
>> -#define MMAP_RND_MASK	(is_32bit_task() ? 0x1fffUL : 0x3ffffUL)
>> -#define STACK_RND_MASK	MMAP_RND_MASK
>> -
>> -struct mm_struct;
>> -extern unsigned long arch_randomize_brk(struct mm_struct *);
>> -#define arch_randomize_brk arch_randomize_brk
>> -
>> +#define STACK_RND_MASK	0x7ff	/* 8MB of VA */
>>
>>   #define ARCH_HAS_SETUP_ADDITIONAL_PAGES 1
>>   struct linux_binprm;
>> diff --git a/arch/parisc/include/asm/processor.h b/arch/parisc/include/asm/processor.h
>> index c05d121cf5d0..982aca20f56f 100644
>> --- a/arch/parisc/include/asm/processor.h
>> +++ b/arch/parisc/include/asm/processor.h
>> @@ -47,6 +47,8 @@
>>
>>   #ifndef __ASSEMBLY__
>>
>> +struct rlimit;
>> +unsigned long mmap_upper_limit(struct rlimit *rlim_stack);
>>   unsigned long calc_max_stack_size(unsigned long stack_max);
>>
>>   /*
>> diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
>> index ab896eff7a1d..98af719d5f85 100644
>> --- a/arch/parisc/kernel/sys_parisc.c
>> +++ b/arch/parisc/kernel/sys_parisc.c
>> @@ -77,7 +77,7 @@ unsigned long calc_max_stack_size(unsigned long stack_max)
>>    * indicating that "current" should be used instead of a passed-in
>>    * value from the exec bprm as done with arch_pick_mmap_layout().
>>    */
>> -static unsigned long mmap_upper_limit(struct rlimit *rlim_stack)
>> +unsigned long mmap_upper_limit(struct rlimit *rlim_stack)
>>   {
>>   	unsigned long stack_base;
>>
>> diff --git a/mm/util.c b/mm/util.c
>> index aa01f6ea5a75..744b4d7e3fae 100644
>> --- a/mm/util.c
>> +++ b/mm/util.c
>> @@ -414,6 +414,15 @@ static int mmap_is_legacy(struct rlimit *rlim_stack)
>>
>>   static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
>>   {
>> +#ifdef CONFIG_STACK_GROWSUP
>> +	/*
>> +	 * For an upwards growing stack the calculation is much simpler.
>> +	 * Memory for the maximum stack size is reserved at the top of the
>> +	 * task. mmap_base starts directly below the stack and grows
>> +	 * downwards.
>> +	 */
>> +	return PAGE_ALIGN_DOWN(mmap_upper_limit(rlim_stack) - rnd);
>> +#else
>>   	unsigned long gap = rlim_stack->rlim_cur;
>>   	unsigned long pad = stack_guard_gap;
>>
>> @@ -431,6 +440,7 @@ static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
>>   		gap = MAX_GAP;
>>
>>   	return PAGE_ALIGN(STACK_TOP - gap - rnd);
>> +#endif
>>   }
>>
>>   void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
>