lkml.org 
[lkml]   [2018]   [Oct]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 02/17] prmem: write rare for static allocation
From
Date


On 26/10/2018 10:41, Peter Zijlstra wrote:
> On Wed, Oct 24, 2018 at 12:34:49AM +0300, Igor Stoppa wrote:
>> +static __always_inline
>
> That's far too large for inline.

The reason for it is that it's supposed to minimize the presence of
gadgets that might be used in JOP attacks.
I am ready to stand corrected, if I'm wrong, but this is the reason why
I did it.

Regarding the function being too large, yes, I would not normally choose
it for inlining.

Actually, I would not normally use "__always_inline" and instead I would
limit myself to plain "inline", at most.

>
>> +bool wr_memset(const void *dst, const int c, size_t n_bytes)
>> +{
>> + size_t size;
>> + unsigned long flags;
>> + uintptr_t d = (uintptr_t)dst;
>> +
>> + if (WARN(!__is_wr_after_init(dst, n_bytes), WR_ERR_RANGE_MSG))
>> + return false;
>> + while (n_bytes) {
>> + struct page *page;
>> + uintptr_t base;
>> + uintptr_t offset;
>> + uintptr_t offset_complement;
>> +
>> + local_irq_save(flags);
>> + page = virt_to_page(d);
>> + offset = d & ~PAGE_MASK;
>> + offset_complement = PAGE_SIZE - offset;
>> + size = min(n_bytes, offset_complement);
>> + base = (uintptr_t)vmap(&page, 1, VM_MAP, PAGE_KERNEL);
>> + if (WARN(!base, WR_ERR_PAGE_MSG)) {
>> + local_irq_restore(flags);
>> + return false;
>> + }
>> + memset((void *)(base + offset), c, size);
>> + vunmap((void *)base);
>
> BUG

yes, somehow I managed to drop this debug configuration from the debug
builds I made.

[...]

> Also, I see an amount of duplication here that shows you're not nearly
> lazy enough.

I did notice a certain amount of duplication, but I didn't know how to
exploit it.

--
igor

\
 
 \ /
  Last update: 2018-10-29 21:02    [W:0.066 / U:21.464 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site