From a07e37121dafd1c2027e7bda1db03bba1d059927 Mon Sep 17 00:00:00 2001
From: Michael Scire <SciresM@gmail.com>
Date: Thu, 15 Nov 2018 18:25:11 -0800
Subject: [PATCH] fs.mitm: loosen boot0 write restrictions, protect keyblobs.

---
 .../fs_mitm/source/fsmitm_boot0storage.cpp    | 50 +++++++++++++++----
 .../fs_mitm/source/fsmitm_boot0storage.hpp    |  5 +-
 .../fs_mitm/source/fsmitm_service.hpp         |  4 +-
 3 files changed, 46 insertions(+), 13 deletions(-)

diff --git a/stratosphere/fs_mitm/source/fsmitm_boot0storage.cpp b/stratosphere/fs_mitm/source/fsmitm_boot0storage.cpp
index e2b25ad40..1554496bd 100644
--- a/stratosphere/fs_mitm/source/fsmitm_boot0storage.cpp
+++ b/stratosphere/fs_mitm/source/fsmitm_boot0storage.cpp
@@ -23,10 +23,6 @@
 static HosMutex g_boot0_mutex;
 static u8 g_boot0_bct_buffer[Boot0Storage::BctEndOffset];
 
-bool Boot0Storage::AllowWrites() {
-    return this->title_id < 0x0100000000001000ULL;
-}
-
 bool Boot0Storage::CanModifyBctPubks() {
     return this->title_id != 0x010000000000001FULL;
 }
@@ -40,18 +36,52 @@ Result Boot0Storage::Read(void *_buffer, size_t size, u64 offset) {
 Result Boot0Storage::Write(void *_buffer, size_t size, u64 offset) {
     std::scoped_lock<HosMutex> lk{g_boot0_mutex};
     
-    if (!AllowWrites()) {
-        return 0x313802;
+    Result rc = 0;
+    u8 *buffer = static_cast<u8 *>(_buffer);
+    
+    /* Protect the keyblob region from writes. */
+    if (offset <= EksStart) {
+        if (offset + size < EksStart) {
+            /* Fall through, no need to do anything here. */
+        } else {
+            if (offset + size < EksEnd) {
+                /* Adjust size to avoid writing end of data. */
+                size = EksStart - offset;
+            } else {
+                /* Perform portion of write falling past end of keyblobs. */
+                const u64 diff = EksEnd - offset;
+                if (R_FAILED((rc = Base::Write(buffer + diff, size - diff, EksEnd)))) {
+                    return rc;
+                }
+                /* Adjust size to avoid writing end of data. */
+                size = EksStart - offset;
+            }
+        }
+    } else {
+        if (offset < EksEnd) {
+            if (offset + size < EksEnd) {
+                /* Ignore writes falling strictly within the region. */
+                return 0;
+            } else {
+                /* Only write past the end of the keyblob region. */
+                buffer = buffer + (EksEnd - offset);
+                size -= (EksEnd - offset);
+                offset = EksEnd;
+            }
+        } else {
+            /* Fall through, no need to do anything here. */
+        }
+    }
+    
+    if (size == 0) {
+        return 0;
     }
     
     /* We care about protecting autorcm from NS. */
     if (CanModifyBctPubks() || offset >= BctEndOffset || (offset + BctSize >= BctEndOffset && offset % BctSize >= BctPubkEnd)) {
-        return Base::Write(_buffer, size, offset);
+        return Base::Write(buffer, size, offset);
     }
     
-    Result rc = 0;
-    u8 *buffer = static_cast<u8 *>(_buffer);
-    
     /* First, let's deal with the data past the end. */
     if (offset + size >= BctEndOffset) {
         const u64 diff = BctEndOffset - offset;
diff --git a/stratosphere/fs_mitm/source/fsmitm_boot0storage.hpp b/stratosphere/fs_mitm/source/fsmitm_boot0storage.hpp
index cf53948f4..b86791ff8 100644
--- a/stratosphere/fs_mitm/source/fsmitm_boot0storage.hpp
+++ b/stratosphere/fs_mitm/source/fsmitm_boot0storage.hpp
@@ -142,10 +142,13 @@ class Boot0Storage : public SectoredProxyStorage<0x200> {
         static constexpr u64 BctPubkStart = 0x210;
         static constexpr u64 BctPubkSize = 0x100;
         static constexpr u64 BctPubkEnd = BctPubkStart + BctPubkSize;
+        
+        static constexpr u64 EksStart = 0x180000;
+        static constexpr u64 EksSize = 0x4000;
+        static constexpr u64 EksEnd = EksStart + EksSize;
     private:
         u64 title_id;
     private:
-        bool AllowWrites();
         bool CanModifyBctPubks();
     public:
         Boot0Storage(FsStorage *s, u64 t) : Base(s), title_id(t) { }
diff --git a/stratosphere/fs_mitm/source/fsmitm_service.hpp b/stratosphere/fs_mitm/source/fsmitm_service.hpp
index 777782b46..fd69bc85a 100644
--- a/stratosphere/fs_mitm/source/fsmitm_service.hpp
+++ b/stratosphere/fs_mitm/source/fsmitm_service.hpp
@@ -41,8 +41,8 @@ class FsMitmService : public IMitmServiceObject {
         }
         
         static bool ShouldMitm(u64 pid, u64 tid) {
-            /* fs.mitm should always mitm everything. */
-            return true;
+            /* fs.mitm should always mitm everything that's not a kip. */
+            return pid >= 0x50;
         }
         
         static void PostProcess(IMitmServiceObject *obj, IpcResponseContext *ctx);