My first UEFI app...

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MatQuasar

Joined: 25 Oct 2023
Posts: 105

MatQuasar 07 May 2024, 17:39

I posted in Discord before but not here.
Anyway, here it is: The shortest "Hello, world" UEFI app, bypassing various structure.

EDIT: Thank you @revolution for the suggestion of "du" instead of "dw".

Code:

format PE64 EFI DLL on 'nul'

section '.code' code readable executable

entry $

       sub     rsp, 40
       mov     rcx, qword [rdx + 0x40]
       lea     rdx, [_message]
       call    qword [rcx + 0x08]
       add     rsp, 40
       retn

_message du 'Hello World',13,10,0

Description:
Filesize:	21.55 KB
Viewed:	2126 Time(s)

Last edited by MatQuasar on 08 May 2024, 01:52; edited 1 time in total

07 May 2024, 17:39

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20630
Location: In your JS exploiting you and your system

revolution 07 May 2024, 22:11

You can use du instead of dw.

Code:

_message du 'Hello World',13,10,0

07 May 2024, 22:11

bitRAKE

Joined: 21 Jul 2003
Posts: 4227
Location: vpcmpistri

bitRAKE 08 May 2024, 00:29

Looks familiar ...
https://github.com/bitRAKE/UEFI_playground/blob/master/examples/amd64/0_hello.asm

_________________
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08 May 2024, 00:29

MatQuasar

Joined: 25 Oct 2023
Posts: 105

MatQuasar 08 May 2024, 01:53

revolution wrote:

You can use du instead of dw.
Code:
_message du 'Hello World',13,10,0    

Nice, I thought it required include file from "encodings". Just now I tested, it doesn't need one. Thank you for the suggestion.

08 May 2024, 01:53

MatQuasar

Joined: 25 Oct 2023
Posts: 105

MatQuasar 08 May 2024, 01:55

bitRAKE wrote:

Looks familiar ...
https://github.com/bitRAKE/UEFI_playground/blob/master/examples/amd64/0_hello.asm

Yes! Actually I referred to your this particular example before doing my own similar one. I use the offset in EFI_SYSTEM_TABLE and EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL directly, skipping the need of include files.

Very Happy

08 May 2024, 01:55

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20630
Location: In your JS exploiting you and your system

revolution 08 May 2024, 02:03

By declaring constants, and expanding the rsp value, this code can be made more reader friendly.

Code:

format PE64 EFI DLL on 'nul'

section '.code' code readable executable

EFI_SYSTEM_TABLE.ConOut                         = 0x40
EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL.OutputString    = 0x08

entry $

        sub     rsp, 8 * 5
        mov     rcx, qword[rdx + EFI_SYSTEM_TABLE.ConOut]
        lea     rdx, [_message]
        call    qword[rcx + EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL.OutputString]
        add     rsp, 8 * 5
        ret

_message du 'Hello World',13,10,0

08 May 2024, 02:03

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