From 526f40caea8797b023e99bde9dbe4040a231bfe1 Mon Sep 17 00:00:00 2001
From: Maciej Szeptuch <neverous@neverous.info>
Date: Sat, 18 May 2024 00:30:27 +0200
Subject: [PATCH] efiboot: prevent overwriting variables with exactly the same
 value

---
 include/efiboot.h                 | 20 ++++++++++++++++++++
 include/efivar-lite/efivar-lite.h |  1 +
 src/efivar-lite.darwin.c          |  5 +++++
 src/efivar-lite.win32.c           |  5 +++++
 4 files changed, 31 insertions(+)

diff --git a/include/efiboot.h b/include/efiboot.h
index 37ea50cb..f3f88b56 100644
--- a/include/efiboot.h
+++ b/include/efiboot.h
@@ -3593,6 +3593,16 @@ inline bool set_variable(const efi_guid_t &guid, const tstring &name, const Vari
     auto [value, attributes] = variable;
     Raw_data bytes;
     size_t size = serialize(bytes, value);
+    // Skip overwriting with exactly the same value
+    if(const auto current = EFIBoot::get_variable<Raw_data>(guid, name); current)
+    {
+        const auto &[current_bytes, current_attributes] = *current;
+        if(current_attributes == attributes && current_bytes == bytes)
+            return true;
+    }
+
+    // Don't care about the error from get_variable
+    efi_error_clear();
     return efi_set_variable(guid, name.c_str(), bytes.data(), size, attributes, mode) == 0;
 }
 
@@ -3602,6 +3612,16 @@ inline bool set_list_variable(const efi_guid_t &guid, const tstring &name, const
     auto [value, attributes] = variable;
     Raw_data bytes;
     size_t size = serialize_list(bytes, value);
+    // Skip overwriting with exactly the same value
+    if(const auto current = EFIBoot::get_variable<Raw_data>(guid, name); current)
+    {
+        const auto &[current_bytes, current_attributes] = *current;
+        if(current_attributes == attributes && current_bytes == bytes)
+            return true;
+    }
+
+    // Don't care about the error from get_variable
+    efi_error_clear();
     return efi_set_variable(guid, name.c_str(), bytes.data(), size, attributes, mode) == 0;
 }
 
diff --git a/include/efivar-lite/efivar-lite.h b/include/efivar-lite/efivar-lite.h
index c6d7f9ed..6ed8ae78 100644
--- a/include/efivar-lite/efivar-lite.h
+++ b/include/efivar-lite/efivar-lite.h
@@ -80,3 +80,4 @@ void efi_set_get_next_variable_name_progress_cb(void (*progress_cb)(size_t, size
 int efi_guid_cmp(const efi_guid_t *a, const efi_guid_t *b);
 
 int efi_error_get(unsigned int n, TCHAR **const filename, TCHAR **const function, int *line, TCHAR **const message, int *error) ATTR_NONNULL(2, 3, 4, 5, 6);
+void efi_error_clear(void);
diff --git a/src/efivar-lite.darwin.c b/src/efivar-lite.darwin.c
index 75669ce5..7252f271 100644
--- a/src/efivar-lite.darwin.c
+++ b/src/efivar-lite.darwin.c
@@ -176,3 +176,8 @@ int efi_error_get(unsigned int n, char **const filename, char **const function,
     *message = mach_error_string(err);
     return 1;
 }
+
+void efi_error_clear(void)
+{
+    // Nothing to do
+}
diff --git a/src/efivar-lite.win32.c b/src/efivar-lite.win32.c
index 83a7517b..a801e5ad 100644
--- a/src/efivar-lite.win32.c
+++ b/src/efivar-lite.win32.c
@@ -215,3 +215,8 @@ int efi_error_get(unsigned int n, TCHAR **const filename, TCHAR **const function
     *message = error_buffer;
     return 1;
 }
+
+void efi_error_clear(void)
+{
+    // Nothing to do
+}