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Re: [PATCH] xen/arm: Fix UBSAN failure in start_xen()
- To: Michal Orzel <michal.orzel@xxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Thu, 8 Feb 2024 15:46:27 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Thu, 08 Feb 2024 15:46:49 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH] xen/arm: Fix UBSAN failure in start_xen()
> On 8 Feb 2024, at 10:43, Michal Orzel <michal.orzel@xxxxxxx> wrote:
>
> When running Xen on arm32, in scenario where Xen is loaded at an address
> such as boot_phys_offset >= 2GB, UBSAN reports the following:
>
> (XEN) UBSAN: Undefined behaviour in arch/arm/setup.c:739:58
> (XEN) pointer operation underflowed 00200000 to 86800000
> (XEN) Xen WARN at common/ubsan/ubsan.c:172
> (XEN) ----[ Xen-4.19-unstable arm32 debug=y ubsan=y Not tainted ]----
> ...
> (XEN) Xen call trace:
> (XEN) [<0031b4c0>] ubsan.c#ubsan_epilogue+0x18/0xf0 (PC)
> (XEN) [<0031d134>] __ubsan_handle_pointer_overflow+0xb8/0xd4 (LR)
> (XEN) [<0031d134>] __ubsan_handle_pointer_overflow+0xb8/0xd4
> (XEN) [<004d15a8>] start_xen+0xe0/0xbe0
> (XEN) [<0020007c>] head.o#primary_switched+0x4/0x30
>
> The failure is reported for the following line:
> (paddr_t)(uintptr_t)(_start + boot_phys_offset)
>
> This occurs because the compiler treats (ptr + size) with size bigger than
> PTRDIFF_MAX as undefined behavior. To address this, switch to macro
> virt_to_maddr(), given the future plans to eliminate boot_phys_offset.
>
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> ---
Hi Michal,
I’ve tested this change with qemu for arm32 and arm64, looks good to me:
Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
Tested-by: Luca Fancellu <luca.fancellu@xxxxxxx>
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