2023-05-17 20:32:14

by Arnd Bergmann

Subject: [PATCH] arm64: kvm: avoid overflow in integer division

From: Arnd Bergmann <[email protected]>

The newly added kvm_mmu_split_nr_page_tables() function uses DIV_ROUND_DOWN_ULL()
to divide 64-bit addresses, but this requires a 32-bit divisior, and PUD_SIZE
may exceed that when 64KB pages are used:

arch/arm64/kvm/mmu.c: In function 'kvm_mmu_split_nr_page_tables':
include/linux/math.h:42:64: error: conversion from 'long unsigned int' to 'u32' {aka 'unsigned int'} changes value from '68719476736' to '0' [-Werror=overflow]
42 | DIV_ROUND_DOWN_ULL((unsigned long long)(ll) + (d) - 1, (d))
| ^~~
include/linux/math.h:39:47: note: in definition of macro 'DIV_ROUND_DOWN_ULL'
39 | #define DIV_ROUND_DOWN_ULL(ll, d) div_u64(ll, d)
| ^
arch/arm64/kvm/mmu.c:95:22: note: in expansion of macro 'DIV_ROUND_UP_ULL'
95 | n += DIV_ROUND_UP_ULL(range, PUD_SIZE);
| ^~~~~~~~~~~~~~~~

Since this code is only used on 64-bit targets, DIV_ROUND_UP() can deal with this
more easily, as it already takes 64-bit arguments.

Fixes: e7bf7a490c68 ("KVM: arm64: Split huge pages when dirty logging is enabled")
Signed-off-by: Arnd Bergmann <[email protected]>
---
arch/arm64/kvm/mmu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 3386bd28d267..6db9ef288ec3 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -92,8 +92,8 @@ static int kvm_mmu_split_nr_page_tables(u64 range)
int n = 0;

if (KVM_PGTABLE_MIN_BLOCK_LEVEL < 2)
- n += DIV_ROUND_UP_ULL(range, PUD_SIZE);
- n += DIV_ROUND_UP_ULL(range, PMD_SIZE);
+ n += DIV_ROUND_UP(range, PUD_SIZE);
+ n += DIV_ROUND_UP(range, PMD_SIZE);
return n;
}

--
2.39.2

2023-05-18 07:33:36

by Marc Zyngier

Subject: Re: [PATCH] arm64: kvm: avoid overflow in integer division

On Wed, 17 May 2023 21:23:39 +0100,
Arnd Bergmann <[email protected]> wrote:
>
> From: Arnd Bergmann <[email protected]>
>
> The newly added kvm_mmu_split_nr_page_tables() function uses DIV_ROUND_DOWN_ULL()
> to divide 64-bit addresses, but this requires a 32-bit divisior, and PUD_SIZE
> may exceed that when 64KB pages are used:
>
> arch/arm64/kvm/mmu.c: In function 'kvm_mmu_split_nr_page_tables':
> include/linux/math.h:42:64: error: conversion from 'long unsigned int' to 'u32' {aka 'unsigned int'} changes value from '68719476736' to '0' [-Werror=overflow]
> 42 | DIV_ROUND_DOWN_ULL((unsigned long long)(ll) + (d) - 1, (d))
> | ^~~
> include/linux/math.h:39:47: note: in definition of macro 'DIV_ROUND_DOWN_ULL'
> 39 | #define DIV_ROUND_DOWN_ULL(ll, d) div_u64(ll, d)
> | ^
> arch/arm64/kvm/mmu.c:95:22: note: in expansion of macro 'DIV_ROUND_UP_ULL'
> 95 | n += DIV_ROUND_UP_ULL(range, PUD_SIZE);
> | ^~~~~~~~~~~~~~~~
>
> Since this code is only used on 64-bit targets, DIV_ROUND_UP() can deal with this
> more easily, as it already takes 64-bit arguments.
>
> Fixes: e7bf7a490c68 ("KVM: arm64: Split huge pages when dirty logging is enabled")
> Signed-off-by: Arnd Bergmann <[email protected]>
> ---
> arch/arm64/kvm/mmu.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 3386bd28d267..6db9ef288ec3 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -92,8 +92,8 @@ static int kvm_mmu_split_nr_page_tables(u64 range)
> int n = 0;
>
> if (KVM_PGTABLE_MIN_BLOCK_LEVEL < 2)
> - n += DIV_ROUND_UP_ULL(range, PUD_SIZE);
> - n += DIV_ROUND_UP_ULL(range, PMD_SIZE);
> + n += DIV_ROUND_UP(range, PUD_SIZE);
> + n += DIV_ROUND_UP(range, PMD_SIZE);
> return n;
> }

This is against -next, right? Oliver, I assume you'll take this as a
fix for Ricardo's series?

Thanks,

M.

--
Without deviation from the norm, progress is not possible.

2023-05-18 12:49:16

by Arnd Bergmann

Subject: Re: [PATCH] arm64: kvm: avoid overflow in integer division

On Thu, May 18, 2023, at 09:30, Marc Zyngier wrote:
> On Wed, 17 May 2023 21:23:39 +0100,
> Arnd Bergmann <[email protected]> wrote:
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index 3386bd28d267..6db9ef288ec3 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -92,8 +92,8 @@ static int kvm_mmu_split_nr_page_tables(u64 range)
>> int n = 0;
>>
>> if (KVM_PGTABLE_MIN_BLOCK_LEVEL < 2)
>> - n += DIV_ROUND_UP_ULL(range, PUD_SIZE);
>> - n += DIV_ROUND_UP_ULL(range, PMD_SIZE);
>> + n += DIV_ROUND_UP(range, PUD_SIZE);
>> + n += DIV_ROUND_UP(range, PMD_SIZE);
>> return n;
>> }
>
> This is against -next, right? Oliver, I assume you'll take this as a
> fix for Ricardo's series?

Yes, correct, I saw it after rebasing my tree from 6.4-rc2 to the
latest -next.

Arnd

2023-05-18 17:49:44

by Oliver Upton

Subject: Re: [PATCH] arm64: kvm: avoid overflow in integer division

On Wed, 17 May 2023 22:23:39 +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <[email protected]>
>
> The newly added kvm_mmu_split_nr_page_tables() function uses DIV_ROUND_DOWN_ULL()
> to divide 64-bit addresses, but this requires a 32-bit divisior, and PUD_SIZE
> may exceed that when 64KB pages are used:
>
> arch/arm64/kvm/mmu.c: In function 'kvm_mmu_split_nr_page_tables':
> include/linux/math.h:42:64: error: conversion from 'long unsigned int' to 'u32' {aka 'unsigned int'} changes value from '68719476736' to '0' [-Werror=overflow]
> 42 | DIV_ROUND_DOWN_ULL((unsigned long long)(ll) + (d) - 1, (d))
> | ^~~
> include/linux/math.h:39:47: note: in definition of macro 'DIV_ROUND_DOWN_ULL'
> 39 | #define DIV_ROUND_DOWN_ULL(ll, d) div_u64(ll, d)
> | ^
> arch/arm64/kvm/mmu.c:95:22: note: in expansion of macro 'DIV_ROUND_UP_ULL'
> 95 | n += DIV_ROUND_UP_ULL(range, PUD_SIZE);
> | ^~~~~~~~~~~~~~~~
>
> [...]

Applied to kvmarm/next, thanks!

[1/1] arm64: kvm: avoid overflow in integer division
https://git.kernel.org/kvmarm/kvmarm/c/14c3555f055d

--
Best,
Oliver