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parisc,metag: Fix crashes due to stack randomization on stack-grows-upwards architectures
On architectures where the stack grows upwards (CONFIG_STACK_GROWSUP=y, currently parisc and metag only) stack randomization sometimes leads to crashes when the stack ulimit is set to lower values than STACK_RND_MASK (which is 8 MB by default if not defined in arch-specific headers). The problem is, that when the stack vm_area_struct is set up in fs/exec.c, the additional space needed for the stack randomization (as defined by the value of STACK_RND_MASK) was not taken into account yet and as such, when the stack randomization code added a random offset to the stack start, the stack effectively got smaller than what the user defined via rlimit_max(RLIMIT_STACK) which then sometimes leads to out-of-stack situations and crashes. This patch fixes it by adding the maximum possible amount of memory (based on STACK_RND_MASK) which theoretically could be added by the stack randomization code to the initial stack size. That way, the user-defined stack size is always guaranteed to be at minimum what is defined via rlimit_max(RLIMIT_STACK). This bug is currently not visible on the metag architecture, because on metag STACK_RND_MASK is defined to 0 which effectively disables stack randomization. The changes to fs/exec.c are inside an "#ifdef CONFIG_STACK_GROWSUP" section, so it does not affect other platformws beside those where the stack grows upwards (parisc and metag). Signed-off-by: Helge Deller <deller@gmx.de> Cc: linux-parisc@vger.kernel.org Cc: James Hogan <james.hogan@imgtec.com> Cc: linux-metag@vger.kernel.org Cc: stable@vger.kernel.org # v3.16+
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@ -348,6 +348,10 @@ struct pt_regs; /* forward declaration... */
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#define ELF_HWCAP 0
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#define STACK_RND_MASK (is_32bit_task() ? \
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0x7ff >> (PAGE_SHIFT - 12) : \
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0x3ffff >> (PAGE_SHIFT - 12))
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struct mm_struct;
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extern unsigned long arch_randomize_brk(struct mm_struct *);
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#define arch_randomize_brk arch_randomize_brk
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@ -77,6 +77,9 @@ static unsigned long mmap_upper_limit(void)
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if (stack_base > STACK_SIZE_MAX)
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stack_base = STACK_SIZE_MAX;
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/* Add space for stack randomization. */
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stack_base += (STACK_RND_MASK << PAGE_SHIFT);
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return PAGE_ALIGN(STACK_TOP - stack_base);
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}
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@ -659,6 +659,9 @@ int setup_arg_pages(struct linux_binprm *bprm,
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if (stack_base > STACK_SIZE_MAX)
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stack_base = STACK_SIZE_MAX;
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/* Add space for stack randomization. */
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stack_base += (STACK_RND_MASK << PAGE_SHIFT);
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/* Make sure we didn't let the argument array grow too large. */
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if (vma->vm_end - vma->vm_start > stack_base)
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return -ENOMEM;
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