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Date: Tue, 17 Apr 2018 09:16:41 +0200
From: Juergen Gross <jgross@...e.com>
To: Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Laura Abbott <labbott@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] x86/xen: Remove use of VLAs
On 16/04/18 15:27, Boris Ostrovsky wrote:
> On 04/13/2018 06:11 PM, Laura Abbott wrote:
>> There's an ongoing effort to remove VLAs[1] from the kernel to eventually
>> turn on -Wvla. The few VLAs in use have an upper bound based on a size
>> of 64K. This doesn't produce an excessively large stack so just switch
>> the upper bound.
>>
>> [1] https://lkml.org/lkml/2018/3/7/621
>>
>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>> ---
>> arch/x86/xen/enlighten_pv.c | 6 ++----
>> 1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
>> index c36d23aa6c35..d96a5a535cbb 100644
>> --- a/arch/x86/xen/enlighten_pv.c
>> +++ b/arch/x86/xen/enlighten_pv.c
>> @@ -421,8 +421,7 @@ static void xen_load_gdt(const struct desc_ptr *dtr)
>> {
>> unsigned long va = dtr->address;
>> unsigned int size = dtr->size + 1;
>> - unsigned pages = DIV_ROUND_UP(size, PAGE_SIZE);
>
>
>
> Isn't dtr->size always either GDT_SIZE or 0?
GDT_SIZE - 1 :-)
>> - unsigned long frames[pages];
>> + unsigned long frames[DIV_ROUND_UP(SZ_64K, PAGE_SIZE)];
So we could just go with one frame and modify the BUG_ON() further below
accordingly.
Juergen
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