How do loop over the search results for a byte string and offset the resultant pointer (in WinDbg)? - windbg

Question

I'm attempting to search for an arbitrarily long byte string in WinDbg and print out the address if an integer in the vicinity meets some criteria.
Pseudo-register $t0 contains the starting address I want to search.
Here's something that, based on the Windows docs, maybe could work (though it clearly doesn't).
.foreach (place { s -[1] #$t0 L?30000 00 00 00 00 00 20 00 00 }) { .if ( (place +0x8) <= 0x1388) { .printf "0x%x\n", place } }
Search
First, the search command doesn't quite work correctly. I only want the address of the match (not the data).
s -[1] #$t0 L?30000 00 00 00 00 00 20 00 00
The docs say that the 1 flag will only return the address. When I issue that command, WinDbg replies
^ Syntax error in 's -1 #$t0 L?30000 00 00 00 00 00 20 00 00 '
If I leave out the -1, it finds two matches.
What am I doing wrong here?
Condition
I don't think the condition is behaving the way I want. I want to look at the third dword starting at place, i.e. place+8, and verify that it's smaller than 5000 (decimal). The .if inside the .foreach isn't printing a meaningful value for place (i.e. the address returned from the search). I think it's dereferencing place first and comparing the value of that integer to 5000. How do I look at the value of, say, *(int*)(place+8)?
Documentation?
The docs are not helping me very much. They only have sparse examples, none of which correspond to what I need.
Is there better documentation somewhere besides MS's Hardware Dev Center?

Answer 1

you can start writing JavaScript for a more legible way of scripting
old way
0:000> s -b vect l?0x1000 4d
00007ff7`8aaa0000 4d 5a 90 00 03 00 00 00-04 00 00 00 ff ff 00 00 MZ..............
00007ff7`8aaa00d4 4d 90 80 d2 df f9 82 d3-4d 90 80 d2 52 69 63 68 M.......M...Rich
00007ff7`8aaa00dc 4d 90 80 d2 52 69 63 68-4c 90 80 d2 00 00 00 00 M...RichL.......
0:000> s -[1]b vect l?0x1000 4d
0x00007ff7`8aaa0000
0x00007ff7`8aaa00d4
0x00007ff7`8aaa00dc
using javascript
function search(addr,len)
{
var index = []
var mem = host.memory.readMemoryValues(addr,len)
for(var i = 0; i < len; i++)
{
if(mem[i] == 0x4d)
{
index.push(addr+i)
}
}
return index
}
executed will return address like which you can manipulate further
0:000> dx -r1 #$scriptContents.search(0x00007ff78aaa0000,1000)
#$scriptContents.search(0x00007ff78aaa0000,1000) : 140701160046592,140701160046804,140701160046812
length : 0x3
[0x0] : 0x7ff78aaa0000
[0x1] : 0x7ff78aaa00d4
[0x2] : 0x7ff78aaa00dc
improving the script a little to find something based on first result
we will try to find the index of Rich string that follows the character 'M'
modified script
function search(addr,len)
{
var index = []
var Rich = []
var result = []
var mem = host.memory.readMemoryValues(addr,len)
for(var i = 0; i < len; i++)
{
if(mem[i] == 0x4d)
{
index.push(addr+i)
var temp = host.memory.readMemoryValues(addr+i+4,1,4)
host.diagnostics.debugLog(temp +"\t")
if(temp == 0x68636952)
{
Rich.push(addr+i)
}
}
}
result.push(index)
result.push(Rich)
return result
}
result only the third occurance of char "M" is followed by Rich string
0:000> dx -r2 #$scriptContents.search(0x00007ff78aaa0000,1000)
3 3548576223 1751345490 #$scriptContents.search(0x00007ff78aaa0000,1000) : 140701160046592,140701160046804,140701160046812,140701160046812
length : 0x2
[0x0] : 140701160046592,140701160046804,140701160046812
length : 0x3
[0x0] : 0x7ff78aaa0000
[0x1] : 0x7ff78aaa00d4
[0x2] : 0x7ff78aaa00dc
[0x1] : 140701160046812
length : 0x1
[0x0] : 0x7ff78aaa00dc
0:000> s -b vect l?0x1000 4d
00007ff7`8aaa0000 4d 5a 90 00 03 00 00 00-04 00 00 00 ff ff 00 00 MZ..............
00007ff7`8aaa00d4 4d 90 80 d2 df f9 82 d3-4d 90 80 d2 52 69 63 68 M.......M...Rich
00007ff7`8aaa00dc 4d 90 80 d2 52 69 63 68-4c 90 80 d2 00 00 00 00 M...RichL.......
load the extensension jsprovider.dll .load jsprovider
write a script say foo.js
load the script .scriptload ...\path\foo.js
execute any functions inside the js you wrote with dx #$scriptContents.myfunc(myargs)
see below using cdb just for ease of copy paste windbg works just as is
F:\>type mojo.js
function hola_mojo ()
{
host.diagnostics.debugLog("hola mojo this is javascript \n")
}
F:\>cdb -c ".load jsprovider;.scriptload .\mojo.js;dx #$scriptContents.hola_mojo();q" cdb | f:\usr\bin\grep.exe -A 6 -i reading
0:000> cdb: Reading initial command '.load jsprovider;.scriptload .\mojo.js;dx #$scriptContents.hola_mojo();q'
JavaScript script successfully loaded from 'F:\mojo.js'
hola mojo this is javascript
#$scriptContents.hola_mojo()
quit:

Answer 2

If I read this part of the documentation
s [-[[Flags]Type]] Range Pattern
correctly, you cannot leave out Type when specifying flags. That's because the flags are inside two square brackets. Otherwise it would have been noted as s [-[Flags][Type]] Range Pattern.
Considering this, the example works:
0:000> .dvalloc 2000
Allocated 2000 bytes starting at 00ba0000
0:000> eb 00ba0000 01 02 03 04 05 06 07 08 09
0:000> eb 00ba1000 01 02 03 04 05 06 07 08 09
0:000> s -[1]b 00ba0000 L?2000 01 02 03 04 05 06 07 08
0x00ba0000
0x00ba1000
Also note that you'll have a hidden bug for the use of place: it should be ${place}. By default, that will work with the address (line break for readability on SO):
0:000> .foreach (place {s -[1]b 00ba0000 L?2000 01 02 03 04 05 06 07 08 })
{ .if ( (${place} +0x8) < 0xba1000) { .printf "0x%x\n", ${place} } }
0xba0000
In order to read a DWord from that address, use the dwo() MASM oerator (line break for readability on SO):
0:000> .foreach (place {s -[1]b 00ba0000 L?2000 01 02 03 04 05 06 07 08 })
{ .if ( (dwo(${place} +0x8)) < 0xba1000)
{ .printf "0x%x = 0x%x\n", ${place}, dwo(${place}+8) } }
0xba0000 = 0x9
0xba1000 = 0x9