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Re: [XEN PATCH] x86/apic: Fix signing in left bitshift
- To: Matthew Barnes <matthew.barnes@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 20 Jun 2024 17:15:44 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 20 Jun 2024 15:16:00 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20.06.2024 16:31, Matthew Barnes wrote:
> There exists a bitshift in the IOAPIC code where a signed integer is
> shifted to the left by at most 31 bits. This is undefined behaviour,
s/at most/up to/ maybe?
> and can cause faults in xtf tests such as pv64-pv-iopl~hypercall.
>
> This patch fixes this by changing the integer from signed to unsigned.
>
> Signed-off-by: Matthew Barnes <matthew.barnes@xxxxxxxxx>
> ---
> xen/arch/x86/io_apic.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/xen/arch/x86/io_apic.c
> +++ b/xen/arch/x86/io_apic.c
> @@ -1756,7 +1756,7 @@ static void cf_check end_level_ioapic_irq_new(struct
> irq_desc *desc, u8 vector)
> !io_apic_level_ack_pending(desc->irq) )
> move_native_irq(desc);
>
> - if (!(v & (1 << (i & 0x1f)))) {
> + if (!(v & (1U << (i & 0x1f)))) {
> spin_lock(&ioapic_lock);
> __mask_IO_APIC_irq(desc->irq);
> __edge_IO_APIC_irq(desc->irq);
For one, can you please also take care of the similar issue in
mask_and_ack_level_ioapic_irq()? And then here and there, can you please
also address the style issue(s) on the line(s) you're touching? In both
cases it will want to be
if ( !(v & (1U << (i & 0x1f))) )
{
thus bringing both fully into proper Xen style afaics. Then:
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Jan
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