From 8297c769e658e953fc72854a7345e65ed8e632cd Mon Sep 17 00:00:00 2001
From: TomAwezome <sonidd1@yahoo.com>
Date: Mon, 12 Sep 2022 00:41:09 -0400
Subject: [PATCH] Fix zealbooter memmap kernel header buffer-overflow.

Previously the zealbooter memmap e820 assignment loop used the entry count value passed via limine, without checking if it was over MEM_E820_ENTRIES_NUM, the #define constant value limit of entries that are stored in the kernel header's e820 region. This commit bumps up the constant entry count to 64 from 48, and also adds a small check in zealbooter to ensure that the entry count value used in the memmap loop caps off at the constant value.
---
 src/Kernel/KernelA.HH   |  4 ++--
 zealbooter/trampoline.S |  3 ---
 zealbooter/zealbooter.c | 20 +++++++++++++++++---
 3 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/src/Kernel/KernelA.HH b/src/Kernel/KernelA.HH
index 56e6fd03..c70c2cb5 100755
--- a/src/Kernel/KernelA.HH
+++ b/src/Kernel/KernelA.HH
@@ -427,7 +427,7 @@ class CSysLimitBase
 };
 
 #help_index "Memory/Info"
-#define MEM_E820_ENTRIES_NUM	48
+#define MEM_E820_ENTRIES_NUM	64
 #define MEM_E820t_USABLE		1
 #define MEM_E820t_RESERVED		2
 #define MEM_E820t_ACPI			3
@@ -4546,4 +4546,4 @@ class CProgress
 #define PRINTF_NEG_E				0x400
 #define PRINTF_NEG_AUX_FORMAT_NUM	0x800
 
-#help_index ""
\ No newline at end of file
+#help_index ""
diff --git a/zealbooter/trampoline.S b/zealbooter/trampoline.S
index c8897ff3..62398b05 100644
--- a/zealbooter/trampoline.S
+++ b/zealbooter/trampoline.S
@@ -5,9 +5,6 @@ trampoline:
     // Set new stack
     mov %rdx, %rsp
 
-//    hlt
-//    hlt
-
     // Load GDTR
     lgdt (%rcx)
 
diff --git a/zealbooter/zealbooter.c b/zealbooter/zealbooter.c
index eab4a057..500165f0 100644
--- a/zealbooter/zealbooter.c
+++ b/zealbooter/zealbooter.c
@@ -44,7 +44,7 @@ struct CDate {
     int32_t date;
 } __attribute__((packed));
 
-#define MEM_E820_ENTRIES_NUM 48
+#define MEM_E820_ENTRIES_NUM 64
 
 #define MEM_E820T_USABLE 1
 #define MEM_E820T_RESERVED 2
@@ -243,8 +243,22 @@ void _start(void) {
 
     kernel->mem_physical_space = 0;
 
+    size_t mem_count = 0;
+    if (memmap_request.response->entry_count > MEM_E820_ENTRIES_NUM)
+    {
+        mem_count = MEM_E820_ENTRIES_NUM;
+        // If limine hands us more regions than the constant, cap it off early instead of buffer overflowing into kernel headers.
+        // This won't guarantee we'll get lucky with framebuffer placement passed via limine.
+        // If the mem_count gets capped at the constant, the system should still boot fully (drive activity lights, reading compiler and code from disc, etc),
+        // just possibly with no visible framebuffer.  :^)
+    }
+    else
+    {
+        mem_count = memmap_request.response->entry_count;
+    }
+
     printf("memory map:\n");
-    for (size_t i = 0; i < memmap_request.response->entry_count; i++) {
+    for (size_t i = 0; i < mem_count; i++) {
         struct limine_memmap_entry *entry = memmap_request.response->entries[i];
         int our_type;
 
@@ -293,7 +307,7 @@ void _start(void) {
     }
     printf("\n");
 
-    kernel->mem_E820[memmap_request.response->entry_count].type = 0;
+    kernel->mem_E820[mem_count].type = 0;
 
     kernel->mem_physical_space = align_up_u64(kernel->mem_physical_space, 0x200000);