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SubjectRe: [PATCH] asm/sections: Check for overflow in memory_contains()
On Tue, Dec 17, 2019 at 11:22:38AM +0100, Vincent Whitchurch wrote:
> ARM uses memory_contains() from its stacktrace code via this function:
>
> static inline bool in_entry_text(unsigned long addr)
> {
> return memory_contains(__entry_text_start, __entry_text_end,
> (void *)addr, 1);
> }
>
> addr is taken from the stack and can be a completely invalid. If addr
> is 0xffffffff, there is an overflow in the pointer arithmetic in
> memory_contains() and in_entry_text() incorrectly returns true.
>
> Fix this by adding an overflow check. The check is done on unsigned
> longs to avoid undefined behaviour.
>
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
> ---
> include/asm-generic/sections.h | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
> index d1779d442aa5..e6e1b381c5df 100644
> --- a/include/asm-generic/sections.h
> +++ b/include/asm-generic/sections.h
> @@ -105,7 +105,15 @@ static inline int arch_is_kernel_initmem_freed(unsigned long addr)
> static inline bool memory_contains(void *begin, void *end, void *virt,
> size_t size)
> {
> - return virt >= begin && virt + size <= end;
> + unsigned long membegin = (unsigned long)begin;
> + unsigned long memend = (unsigned long)end;
> + unsigned long objbegin = (unsigned long)virt;
> + unsigned long objend = objbegin + size;
> +
> + if (objend < objbegin)
> + return false;
> +
> + return objbegin >= membegin && objend <= memend;

Would merely changing to:

return virt >= begin && virt <= end - size;

be sufficient ? Is end - size possible to underflow?

> }
>
> /**
> --
> 2.20.0
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

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