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Re: [PATCH] xsm/flask: Fix undefined behaviour in avc_dump_av()
- To: Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 1 May 2026 15:27:25 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 01 May 2026 14:27:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 01/05/2026 3:17 pm, Dmytro Prokopchuk1 wrote:
> When booting Xen with CONFIG_USBAN=y and CONFIG_XSM_FLASK=y,
> UBSAN reports undefined behaviour in avc_dump_av() due to a left
> shift on a signed int:
>
> (XEN) [ 1.104348]
> ================================================================================
> (XEN) [ 1.105096] UBSAN: Undefined behaviour in xsm/flask/avc.c:184:14
> (XEN) [ 1.106052] left shift of 1073741824 by 1 places cannot be
> represented in type 'int'
> (XEN) [ 1.107546] Xen WARN at common/ubsan/ubsan.c:176
> (XEN) [ 1.108295] ----[ Xen-4.21.1 arm64 debug=y ubsan=y Not tainted
> ]----
> (XEN) [ 1.108848] CPU: 0
> (XEN) [ 1.109147] PC: 00000a00002f64fc ubsan.c#ubsan_epilogue+0x10/0xd4
> [...]
> (XEN) [ 1.146320] Xen call trace:
> (XEN) [ 1.146663] [<00000a00002f64fc>] ubsan.c#ubsan_epilogue+0x10/0xd4
> (PC)
> (XEN) [ 1.147227] [<00000a00002f7bc4>]
> __ubsan_handle_shift_out_of_bounds+0x1a0/0x290 (LR)
> (XEN) [ 1.147868]
> (XEN) [ 1.148177]
> ================================================================================
>
> This can be solved by making 'perm' an unsigned 32-bit type (u32).
>
> Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@xxxxxxxx>
> ---
> Test CI pipeline:
> https://gitlab.com/xen-project/people/dimaprkp4k/xen/-/pipelines/2493649109
> ---
> xen/xsm/flask/avc.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/xen/xsm/flask/avc.c b/xen/xsm/flask/avc.c
> index 3d39e55cae..9c3ffdc070 100644
> --- a/xen/xsm/flask/avc.c
> +++ b/xen/xsm/flask/avc.c
> @@ -152,7 +152,8 @@ static void __attribute__ ((format (printf, 2, 3)))
> */
> static void avc_dump_av(struct avc_dump_buf *buf, u16 tclass, u32 av)
> {
> - int i, i2, perm;
> + int i, i2;
> + u32 perm;
>
> if ( av == 0 )
> {
The fix is fine, but wants to be uint32_t. (The existing code is
already inconsistent, and wants fixing up towards Xen's preferred style.)
Can be fixed on commit.
~Andrew
|
