doc: remove Security section from build-unix.md

Our compile documentation isn't the right place for genric binary
hardening notes, which are neither particularly Bitcoin-Core specific,
or as relevant as they might have once been, i.e non-executable stacks
are now just the norm.

Just remove the notes for now, if someone has
something more interesting/Bitcoin Core specific, it could be added in
separate documentation in the future (maybe into the devwiki or
similar).

Split from
https://github.com/bitcoin/bitcoin/pull/27685#discussion_r1196517868.
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fanquake 2023-05-17 14:36:27 +01:00
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@ -184,52 +184,6 @@ export BDB_PREFIX="/path/to/bitcoin/depends/x86_64-pc-linux-gnu"
**Note**: You only need Berkeley DB if the legacy wallet is enabled (see [*Disable-wallet mode*](#disable-wallet-mode)).
Security
--------
To help make your Bitcoin Core installation more secure by making certain attacks impossible to
exploit even if a vulnerability is found, binaries are hardened by default.
This can be disabled with:
Hardening Flags:
./configure --enable-hardening
./configure --disable-hardening
Hardening enables the following features:
* _Position Independent Executable_: Build position independent code to take advantage of Address Space Layout Randomization
offered by some kernels. Attackers who can cause execution of code at an arbitrary memory
location are thwarted if they don't know where anything useful is located.
The stack and heap are randomly located by default, but this allows the code section to be
randomly located as well.
On an AMD64 processor where a library was not compiled with -fPIC, this will cause an error
such as: "relocation R_X86_64_32 against `......' can not be used when making a shared object;"
To test that you have built PIE executable, install scanelf, part of paxutils, and use:
scanelf -e ./bitcoin
The output should contain:
TYPE
ET_DYN
* _Non-executable Stack_: If the stack is executable then trivial stack-based buffer overflow exploits are possible if
vulnerable buffers are found. By default, Bitcoin Core should be built with a non-executable stack,
but if one of the libraries it uses asks for an executable stack or someone makes a mistake
and uses a compiler extension which requires an executable stack, it will silently build an
executable without the non-executable stack protection.
To verify that the stack is non-executable after compiling use:
`scanelf -e ./bitcoin`
The output should contain:
STK/REL/PTL
RW- R-- RW-
The STK RW- means that the stack is readable and writeable but not executable.
Disable-wallet mode
--------------------
When the intention is to only run a P2P node, without a wallet, Bitcoin Core can