From 780c69c17e3668400bfdaaa84925de681e0d1ba7 Mon Sep 17 00:00:00 2001
From: Amelia Coutard <eliottulio.coutard@gmail.com>
Date: Tue, 28 Feb 2023 23:24:56 +0100
Subject: [PATCH] Added a doc.txt file to specify the kernel documentation, and
 added a corresponding assert in the code

Currently, the documentation specifies how virtual memory is used.
The added assert ensures that any loaded elf program's segments are within the specified bounds.
---
 doc.txt               | 10 ++++++++++
 kernel/src/kernel.cpp |  3 +++
 2 files changed, 13 insertions(+)
 create mode 100644 doc.txt

diff --git a/doc.txt b/doc.txt
new file mode 100644
index 0000000..6e9714c
--- /dev/null
+++ b/doc.txt
@@ -0,0 +1,10 @@
+(Virtual) memory map:
+
+0000'0000'0000'0000 ↔ 0000'0000'0000'1000 - unmapped: 4KiB ensure that nullptr causes a page fault if accessed.
+0000'0000'0000'1000 ↔ 0000'0010'0000'0000 - program segments (.text, .data, .bss, etc.): 64GiB - 4KiB
+0000'0010'0000'1000 ↔ 0000'7FFF'FFFF'0000 - heap: 128TiB - 64GiB - 64KiB
+0000'7FFF'FFFF'0000 ↔ 0000'8000'0000'0000 - stack: 64KiB
+-- Invalid addresses --
+FFFF'8000'0000'0000 ↔ FFFF'C000'0000'0000 - physical memory: 64TiB
+FFFF'C000'0000'0000 ↔ FFFF'FFFF'8000'0000 - unmapped: 64TiB - 2GiB
+FFFF'FFFF'8000'0000 ↔10000'0000'0000'0000 - kernel: 2GiB
diff --git a/kernel/src/kernel.cpp b/kernel/src/kernel.cpp
index e5c5b8b..478783d 100644
--- a/kernel/src/kernel.cpp
+++ b/kernel/src/kernel.cpp
@@ -201,6 +201,9 @@ extern "C" void kmain(unsigned long magic, os::phys_ptr<const multiboot2::info_s
 		}
 		os::print("Segment: loadable\n");
 		os::assert((std::uintptr_t(program_header.p_vaddr) & 0xFFF) == 0, "Program segment not 4KiB aligned.");
+		os::assert(0x1000 <= std::uint64_t(program_header.p_vaddr)
+				&& std::uint64_t(program_header.p_vaddr + program_header.p_memsz) < 0x10'0000'0000,
+			"Program segments must be contained between 0x1000 and 0x10'0000'0000 (i.e. 64GiB).");
 
 		// Allocate memory for segment:
 		std::size_t nb_pages = (program_header.p_memsz + 0x1000) / 0x1000;
-- 
2.47.0