From 3c6b779323a5d3d7bcdeb614d6f7635a973d21ae Mon Sep 17 00:00:00 2001
From: James Hilliard <james.hilliard1@gmail.com>
Date: Mon, 9 Nov 2026 15:53:57 -0700
Subject: [PATCH] tools: Add BCM2712 RAM authenticity check

Compare the RAM capacity in the running board revision with the factory
revision in OTP row 32. Report possible RAM tampering or replacement and
advise contacting the seller to arrange a return.

Return distinct statuses for matching, mismatched, and unavailable
capacity information. Explain that matching capacity cannot establish
that the RAM is original.
---
 tools/rpi-ram-authenticity-check | 76 ++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100755 tools/rpi-ram-authenticity-check

diff --git a/tools/rpi-ram-authenticity-check b/tools/rpi-ram-authenticity-check
new file mode 100755
index 00000000..ead65bba
--- /dev/null
+++ b/tools/rpi-ram-authenticity-check
@@ -0,0 +1,76 @@
+#!/bin/sh
+
+# Compare BCM2712's reported RAM capacity with its factory revision in OTP.
+set -ef
+
+usage() {
+   cat <<EOF
+Usage: rpi-ram-authenticity-check [-h | --help]
+
+Compare the RAM capacity in the running board revision with the factory
+capacity in BCM2712 OTP row 32. Requires vcgencmd and access to /dev/vcio.
+This is a read-only capacity check; it cannot prove that the RAM is original
+or detect a replacement with the same capacity.
+
+Exit status: 0 = capacity matches, 1 = capacity differs, 2 = unable to check.
+EOF
+}
+
+die() {
+   echo "Unable to check RAM: $*" >&2
+   exit 2
+}
+
+ramSizeFromRevision() {
+   case "$1" in
+      ''|*[!0-9a-fA-F]*) return 1 ;;
+   esac
+   [ "${#1}" -le 8 ] || return 1
+   # Require a new-style BCM2712 revision before interpreting its RAM field.
+   [ $(((0x$1 >> 23) & 1)) -eq 1 ] &&
+      [ $(((0x$1 >> 12) & 15)) -eq 4 ] || return 1
+   ram_code=$(((0x$1 >> 20) & 7))
+   # Code 7 means "Other", not 32 GiB.
+   [ "${ram_code}" -lt 7 ] || return 1
+   echo "$((256 << ram_code))"
+}
+
+if [ "$#" -ne 0 ]; then
+   if [ "$#" -eq 1 ] && { [ "$1" = -h ] || [ "$1" = --help ]; }; then
+      usage
+      exit 0
+   fi
+   usage >&2
+   exit 2
+fi
+
+# Use the same running revision sources as rpi-eeprom-update. Do not fall
+# back to OTP here: comparing the factory value with itself would miss changes.
+dt_revision=/sys/firmware/devicetree/base/system/linux,revision
+if [ -r "${dt_revision}" ]; then
+   [ "$(wc -c < "${dt_revision}")" -eq 4 ] || die "Invalid device-tree board revision."
+   board_revision=$(od -v -An -t x1 "${dt_revision}" | tr -d ' \n')
+elif [ -r /proc/cpuinfo ]; then
+   board_revision=$(sed -n '/^Revision/s/^.*: \(.*\)/\1/p' /proc/cpuinfo)
+else
+   die "No running board revision found."
+fi
+reported_mib=$(ramSizeFromRevision "${board_revision}") ||
+   die "The running board revision must describe a BCM2712 device with a known RAM capacity."
+
+command -v vcgencmd > /dev/null || die "vcgencmd is required to read the factory RAM capacity."
+otp_dump=$(vcgencmd otp_dump) || die "Failed to read OTP; check access to /dev/vcio."
+# Row 32 is the BCM2712 factory revision; BCM2711 uses row 30.
+factory_revision=$(printf '%s\n' "${otp_dump}" | sed -n 's/^32:\([0-9a-fA-F]\{8\}\)$/\1/p')
+factory_mib=$(ramSizeFromRevision "${factory_revision}") ||
+   die "OTP row 32 does not contain a valid BCM2712 revision with a known RAM capacity."
+
+echo "Factory RAM: ${factory_mib} MiB; reported RAM: ${reported_mib} MiB."
+if [ "${factory_mib}" -eq "${reported_mib}" ]; then
+   echo "RAM appears authentic: capacity matches the factory configuration."
+   exit 0
+fi
+
+echo "WARNING: RAM capacity mismatch detected: possible RAM tampering or replacement." >&2
+echo "Contact the seller to arrange a return." >&2
+exit 1