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How can I mod binary values (bitflags) with assembly?

 
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Fatamorgen
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PostPosted: Tue Feb 22, 2022 3:45 pm    Post subject: How can I mod binary values (bitflags) with assembly? Reply with quote
I want to inject a code using the assembly but I need only to change a bit flag on the address linked to it. The main problem is that I can only change bytes and not bit flags. Is there a way to change only the bitflags?
I want to change bit 7 only and not the entire byte.

Code:
define(address,"EEtc.exe"+1FE3B)
define(bytes,8B 86 AC 00 00 00)

[ENABLE]

assert(address,bytes)
alloc(newmem,$100)

label(code)
label(return)

newmem:

code:
  mov eax,[esi+000000AC]  //Something like mov binary ptr 7 [esi+000000AC],1
  jmp return

address:
  jmp newmem
  nop
return:

[DISABLE]

address:
  db bytes
dealloc(newmem)
[/code]
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ParkourPenguin
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PostPosted: Tue Feb 22, 2022 5:14 pm    Post subject: Reply with quote
Memory can only be accessed up to a byte granularity

Use the instructions and, or, xor to unset, set, and flip bits respectively:
Code:
or byte ptr[esi+AC],80

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Dark Byte
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PostPosted: Tue Feb 22, 2022 5:29 pm    Post subject: Reply with quote
or:
Code:

bts [esi+ac],7

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Fatamorgen
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PostPosted: Wed Feb 23, 2022 8:39 am    Post subject: Reply with quote
Worked like a charm. Thanks Peng and Dark
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