Commit c603a309 authored Jun 19, 2019 by Thomas Lendacky Committed by Borislav Petkov Jun 20, 2019

x86/mm: Identify the end of the kernel area to be reserved



The memory occupied by the kernel is reserved using memblock_reserve()
in setup_arch(). Currently, the area is from symbols _text to __bss_stop.
Everything after __bss_stop must be specifically reserved otherwise it
is discarded. This is not clearly documented.

Add a new symbol, __end_of_kernel_reserve, that more readily identifies
what is reserved, along with comments that indicate what is reserved,
what is discarded and what needs to be done to prevent a section from
being discarded.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Tested-by: Lianbo Jiang <lijiang@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <rrichter@marvell.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Sinan Kaya <okaya@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "x86@kernel.org" <x86@kernel.org>
Link: https://lkml.kernel.org/r/7db7da45b435f8477f25e66f292631ff766a844c.1560969363.git.thomas.lendacky@amd.com

parent 9e0babf2

arch/x86/include/asm/sections.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -13,4 +13,6 @@ extern char __end_rodata_aligned[];
		extern char __end_rodata_hpage_align[];
		#endif

		extern char __end_of_kernel_reserve[];

		#endif /* _ASM_X86_SECTIONS_H */

arch/x86/kernel/setup.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -827,8 +827,14 @@ dump_kernel_offset(struct notifier_block self, unsigned long v, void p)

		void __init setup_arch(char **cmdline_p)
		{
		/*
		* Reserve the memory occupied by the kernel between _text and
		* __end_of_kernel_reserve symbols. Any kernel sections after the
		* __end_of_kernel_reserve symbol must be explicitly reserved with a
		* separate memblock_reserve() or they will be discarded.
		*/
		memblock_reserve(__pa_symbol(_text),
		(unsigned long)__bss_stop - (unsigned long)_text);
		(unsigned long)__end_of_kernel_reserve - (unsigned long)_text);

		/*
		* Make sure page 0 is always reserved because on systems with

arch/x86/kernel/vmlinux.lds.S

+8 −1

Original line number	Diff line number	Diff line
		@@ -368,6 +368,14 @@ SECTIONS
		__bss_stop = .;
		}

		/*
		* The memory occupied from _text to here, __end_of_kernel_reserve, is
		* automatically reserved in setup_arch(). Anything after here must be
		* explicitly reserved using memblock_reserve() or it will be discarded
		* and treated as available memory.
		*/
		__end_of_kernel_reserve = .;

		. = ALIGN(PAGE_SIZE);
		.brk : AT(ADDR(.brk) - LOAD_OFFSET) {
		__brk_base = .;
		@@ -382,7 +390,6 @@ SECTIONS
		STABS_DEBUG
		DWARF_DEBUG

		/* Sections to be discarded */
		DISCARDS
		/DISCARD/ : {
		*(.eh_frame)

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