x86/apic: Fix signed shift in io_apic.c

[XEN PATCH v2] x86/apic: Fix signed shift in io_apic.c

Posted by Matthew Barnes 5 months ago

There exists bitshifts in the IOAPIC code where signed integers are
shifted to the left by up to 31 bits, which is undefined behaviour.

This patch fixes this by changing the integers from signed to unsigned.

Signed-off-by: Matthew Barnes <matthew.barnes@cloud.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
Changes in v2:
- Correct signed shifting in mask_and_ack_level_ioapic_irq()
- Adjust bracket spacing to uphold Xen style
- Improve commit message
---
 xen/arch/x86/io_apic.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c
index b48a64246548..d9070601a26f 100644
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -1692,7 +1692,7 @@ static void cf_check mask_and_ack_level_ioapic_irq(struct irq_desc *desc)
        !io_apic_level_ack_pending(desc->irq))
         move_masked_irq(desc);
 
-    if ( !(v & (1 << (i & 0x1f))) ) {
+    if ( !(v & (1U << (i & 0x1f))) ) {
         spin_lock(&ioapic_lock);
         __edge_IO_APIC_irq(desc->irq);
         __level_IO_APIC_irq(desc->irq);
@@ -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);
-- 
2.34.1

Re: [XEN PATCH for-4.19? v2] x86/apic: Fix signed shift in io_apic.c

Posted by Jan Beulich 5 months ago

On 20.06.2024 17:36, Matthew Barnes wrote:
> There exists bitshifts in the IOAPIC code where signed integers are
> shifted to the left by up to 31 bits, which is undefined behaviour.
> 
> This patch fixes this by changing the integers from signed to unsigned.
> 
> Signed-off-by: Matthew Barnes <matthew.barnes@cloud.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>

Only almost, ...

> ---
> Changes in v2:
> - Correct signed shifting in mask_and_ack_level_ioapic_irq()
> - Adjust bracket spacing to uphold Xen style

... as that was only half of what I had asked for. The other half was ...

> --- a/xen/arch/x86/io_apic.c
> +++ b/xen/arch/x86/io_apic.c
> @@ -1692,7 +1692,7 @@ static void cf_check mask_and_ack_level_ioapic_irq(struct irq_desc *desc)
>         !io_apic_level_ack_pending(desc->irq))
>          move_masked_irq(desc);
>  
> -    if ( !(v & (1 << (i & 0x1f))) ) {
> +    if ( !(v & (1U << (i & 0x1f))) ) {
>          spin_lock(&ioapic_lock);
>          __edge_IO_APIC_irq(desc->irq);
>          __level_IO_APIC_irq(desc->irq);
> @@ -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);

... to put each opening figure brace on their own line. I guess Andrew or
I will do that while committing then.

Jan

Re: [XEN PATCH for-4.19? v2] x86/apic: Fix signed shift in io_apic.c

Posted by Andrew Cooper 5 months ago

On 20/06/2024 4:40 pm, Jan Beulich wrote:
> On 20.06.2024 17:36, Matthew Barnes wrote:
>> There exists bitshifts in the IOAPIC code where signed integers are
>> shifted to the left by up to 31 bits, which is undefined behaviour.
>>
>> This patch fixes this by changing the integers from signed to unsigned.
>>
>> Signed-off-by: Matthew Barnes <matthew.barnes@cloud.com>
>> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> Only almost, ...
>
>> ---
>> Changes in v2:
>> - Correct signed shifting in mask_and_ack_level_ioapic_irq()
>> - Adjust bracket spacing to uphold Xen style
> ... as that was only half of what I had asked for. The other half was ...
>
>> --- a/xen/arch/x86/io_apic.c
>> +++ b/xen/arch/x86/io_apic.c
>> @@ -1692,7 +1692,7 @@ static void cf_check mask_and_ack_level_ioapic_irq(struct irq_desc *desc)
>>         !io_apic_level_ack_pending(desc->irq))
>>          move_masked_irq(desc);
>>  
>> -    if ( !(v & (1 << (i & 0x1f))) ) {
>> +    if ( !(v & (1U << (i & 0x1f))) ) {
>>          spin_lock(&ioapic_lock);
>>          __edge_IO_APIC_irq(desc->irq);
>>          __level_IO_APIC_irq(desc->irq);
>> @@ -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);
> ... to put each opening figure brace on their own line. I guess Andrew or
> I will do that while committing then.

Yeah.  That can be fixed on commit.

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>