From 3af575bcad8a1d700b97bb8bac81db6763f5c5a9 Mon Sep 17 00:00:00 2001
From: Steve Muckle <smuckle@google.com>
Date: Thu, 18 Jun 2020 17:02:15 -0700
Subject: [PATCH] fastboot: copy AVB footer on boot image to end of partition

If the flashed boot image is smaller than the block device, the AVB
footer will not be at the end of the partition. Although images are
normally created to match the partition size the GKI boot.img must work
on all devices, and the size of the boot partition will vary.

Copy the AVB footer to the end of the partition before flashing, if it
is not there already.

Bug: 159377163
Change-Id: I5a5e25fb54dc9d6a2930fda63434968808ffa1f0
---
 fastboot/fastboot.cpp | 68 +++++++++++++++++++++++++++++++++++++------
 1 file changed, 59 insertions(+), 9 deletions(-)

diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index 0e9713d4a..86cf30df2 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -992,10 +992,69 @@ static bool has_vbmeta_partition() {
            fb->GetVar("partition-type:vbmeta_b", &partition_type) == fastboot::SUCCESS;
 }
 
+static std::string fb_fix_numeric_var(std::string var) {
+    // Some bootloaders (angler, for example), send spurious leading whitespace.
+    var = android::base::Trim(var);
+    // Some bootloaders (hammerhead, for example) use implicit hex.
+    // This code used to use strtol with base 16.
+    if (!android::base::StartsWith(var, "0x")) var = "0x" + var;
+    return var;
+}
+
+static void copy_boot_avb_footer(const std::string& partition, struct fastboot_buffer* buf) {
+    if (buf->sz < AVB_FOOTER_SIZE) {
+        return;
+    }
+
+    std::string partition_size_str;
+    if (fb->GetVar("partition-size:" + partition, &partition_size_str) != fastboot::SUCCESS) {
+        die("cannot get boot partition size");
+    }
+
+    partition_size_str = fb_fix_numeric_var(partition_size_str);
+    int64_t partition_size;
+    if (!android::base::ParseInt(partition_size_str, &partition_size)) {
+        die("Couldn't parse partition size '%s'.", partition_size_str.c_str());
+    }
+    if (partition_size == buf->sz) {
+        return;
+    }
+    if (partition_size < buf->sz) {
+        die("boot partition is smaller than boot image");
+    }
+
+    std::string data;
+    if (!android::base::ReadFdToString(buf->fd, &data)) {
+        die("Failed reading from boot");
+    }
+
+    uint64_t footer_offset = buf->sz - AVB_FOOTER_SIZE;
+    if (0 != data.compare(footer_offset, AVB_FOOTER_MAGIC_LEN, AVB_FOOTER_MAGIC)) {
+        return;
+    }
+
+    int fd = make_temporary_fd("boot rewriting");
+    if (!android::base::WriteStringToFd(data, fd)) {
+        die("Failed writing to modified boot");
+    }
+    lseek(fd, partition_size - AVB_FOOTER_SIZE, SEEK_SET);
+    if (!android::base::WriteStringToFd(data.substr(footer_offset), fd)) {
+        die("Failed copying AVB footer in boot");
+    }
+    close(buf->fd);
+    buf->fd = fd;
+    buf->sz = partition_size;
+    lseek(fd, 0, SEEK_SET);
+}
+
 static void flash_buf(const std::string& partition, struct fastboot_buffer *buf)
 {
     sparse_file** s;
 
+    if (partition == "boot" || partition == "boot_a" || partition == "boot_b") {
+        copy_boot_avb_footer(partition, buf);
+    }
+
     // Rewrite vbmeta if that's what we're flashing and modification has been requested.
     if (g_disable_verity || g_disable_verification) {
         if (partition == "vbmeta" || partition == "vbmeta_a" || partition == "vbmeta_b") {
@@ -1491,15 +1550,6 @@ static void do_oem_command(const std::string& cmd, std::vector<std::string>* arg
     fb->RawCommand(command, "");
 }
 
-static std::string fb_fix_numeric_var(std::string var) {
-    // Some bootloaders (angler, for example), send spurious leading whitespace.
-    var = android::base::Trim(var);
-    // Some bootloaders (hammerhead, for example) use implicit hex.
-    // This code used to use strtol with base 16.
-    if (!android::base::StartsWith(var, "0x")) var = "0x" + var;
-    return var;
-}
-
 static unsigned fb_get_flash_block_size(std::string name) {
     std::string sizeString;
     if (fb->GetVar(name, &sizeString) != fastboot::SUCCESS || sizeString.empty()) {