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Re: Memory Protections

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Am 14.07.2020 um 12:21 schrieb George Neuner:
> On Mon, 13 Jul 2020 13:30:16 -0700, Don Y
>> For no-execute, I don't see any use beyond that of enhancing
>> confidence in the codebase; I don't see any *features* that
>> rely on detecting "legal" attempts to execute particular
>> regions of memory (assuming execute-access is treated as
>> a special case of read-access).
>>
>> The ONE question I am posing here is "are there any?"
> 
> I'm not sure what you're getting at here: what would be a "legal"
> attempt to execute NX protected memory?
> 
> Obviously something like a JIT compiler needs to be able to switch off
> NX for the code buffer so a program can execute it ... but there's no
> point to allowing access before the code is ready.

The "+1" of a JIT compiler would be a virtualisation solution that has
paged in the whole guest system already, but wants to analyze or
redirect attempts to execute code.

As I understand, older virtualisation solutions for x86 worked that way
because x86 has some instructions that you want to virtualize but that
do not trap on older processors (e.g. sgdt, str). You had to play some
extra tricks because x86 originally didn't have per-page NX bits.


  Stefan

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Thread

Memory Protections Don Y <blockedofcourse@foo.invalid> - 2020-07-13 13:30 -0700
  Re: Memory Protections Don Y <blockedofcourse@foo.invalid> - 2020-07-13 23:45 -0700
    Re: Memory Protections Theo <theom+news@chiark.greenend.org.uk> - 2020-07-14 10:40 +0100
      Re: Memory Protections Don Y <blockedofcourse@foo.invalid> - 2020-07-14 11:44 -0700
      Re: Memory Protections mac <acolvin@efunct.com> - 2020-07-19 15:03 +0000
  Re: Memory Protections George Neuner <gneuner2@comcast.net> - 2020-07-14 06:21 -0400
    Re: Memory Protections Stefan Reuther <stefan.news@arcor.de> - 2020-07-14 18:17 +0200
    Re: Memory Protections Don Y <blockedofcourse@foo.invalid> - 2020-07-14 11:48 -0700
      Re: Memory Protections George Neuner <gneuner2@comcast.net> - 2020-07-16 02:02 -0400
        Re: Memory Protections Don Y <blockedofcourse@foo.invalid> - 2020-07-17 18:25 -0700

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