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From: "tip-bot2 for Ard Biesheuvel" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Kees Cook <keescook@chromium.org>, Ingo Molnar <mingo@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Sedat Dilek <sedat.dilek@gmail.com>, x86 <x86@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: [tip: x86/boot] x86/boot/compressed: Get rid of GOT fixup code
Date: Fri, 14 Aug 2020 15:23:40 -0000
Message-ID: <159741862017.3192.5772162309097866591.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20200731230820.1742553-4-keescook@chromium.org>

The following commit has been merged into the x86/boot branch of tip:

Commit-ID:     423e4d198a036689de73fd6b073fc4349c4fa1ee
Gitweb:        https://git.kernel.org/tip/423e4d198a036689de73fd6b073fc4349c4fa1ee
Author:        Ard Biesheuvel <ardb@kernel.org>
AuthorDate:    Fri, 31 Jul 2020 16:07:47 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 14 Aug 2020 12:52:35 +02:00

x86/boot/compressed: Get rid of GOT fixup code

In a previous patch, we have eliminated GOT entries from the decompressor
binary and added an assertion that the .got section is empty. This means
that the GOT fixup routines that exist in both the 32-bit and 64-bit
startup routines have become dead code, and can be removed.

While at it, drop the KEEP() from the linker script, as it has no effect
on the contents of output sections that are created by the linker itself.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200731230820.1742553-4-keescook@chromium.org
---
 arch/x86/boot/compressed/head_32.S     | 24 +----------
 arch/x86/boot/compressed/head_64.S     | 57 +-------------------------
 arch/x86/boot/compressed/vmlinux.lds.S |  4 +--
 3 files changed, 5 insertions(+), 80 deletions(-)

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 03557f2..39f0bb4 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -49,16 +49,13 @@
  * Position Independent Executable (PIE) so that linker won't optimize
  * R_386_GOT32X relocation to its fixed symbol address.  Older
  * linkers generate R_386_32 relocations against locally defined symbols,
- * _bss, _ebss, _got, _egot and _end, in PIE.  It isn't wrong, just less
- * optimal than R_386_RELATIVE.  But the x86 kernel fails to properly handle
- * R_386_32 relocations when relocating the kernel.  To generate
- * R_386_RELATIVE relocations, we mark _bss, _ebss, _got, _egot and _end as
- * hidden:
+ * _bss, _ebss and _end, in PIE.  It isn't wrong, just less optimal than
+ * R_386_RELATIVE.  But the x86 kernel fails to properly handle R_386_32
+ * relocations when relocating the kernel.  To generate R_386_RELATIVE
+ * relocations, we mark _bss, _ebss and _end as hidden:
  */
 	.hidden _bss
 	.hidden _ebss
-	.hidden _got
-	.hidden _egot
 	.hidden _end
 
 	__HEAD
@@ -193,19 +190,6 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
 	rep	stosl
 
 /*
- * Adjust our own GOT
- */
-	leal	_got(%ebx), %edx
-	leal	_egot(%ebx), %ecx
-1:
-	cmpl	%ecx, %edx
-	jae	2f
-	addl	%ebx, (%edx)
-	addl	$4, %edx
-	jmp	1b
-2:
-
-/*
  * Do the extraction, and jump to the new kernel..
  */
 				/* push arguments for extract_kernel: */
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 97d37f0..bf1ab30 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -40,8 +40,6 @@
  */
 	.hidden _bss
 	.hidden _ebss
-	.hidden _got
-	.hidden _egot
 	.hidden _end
 
 	__HEAD
@@ -354,25 +352,6 @@ SYM_CODE_START(startup_64)
 	leaq	boot_stack_end(%rbx), %rsp
 
 	/*
-	 * paging_prepare() and cleanup_trampoline() below can have GOT
-	 * references. Adjust the table with address we are running at.
-	 *
-	 * Zero RAX for adjust_got: the GOT was not adjusted before;
-	 * there's no adjustment to undo.
-	 */
-	xorq	%rax, %rax
-
-	/*
-	 * Calculate the address the binary is loaded at and use it as
-	 * a GOT adjustment.
-	 */
-	call	1f
-1:	popq	%rdi
-	subq	$1b, %rdi
-
-	call	.Ladjust_got
-
-	/*
 	 * At this point we are in long mode with 4-level paging enabled,
 	 * but we might want to enable 5-level paging or vice versa.
 	 *
@@ -464,21 +443,6 @@ trampoline_return:
 	pushq	$0
 	popfq
 
-	/*
-	 * Previously we've adjusted the GOT with address the binary was
-	 * loaded at. Now we need to re-adjust for relocation address.
-	 *
-	 * Calculate the address the binary is loaded at, so that we can
-	 * undo the previous GOT adjustment.
-	 */
-	call	1f
-1:	popq	%rax
-	subq	$1b, %rax
-
-	/* The new adjustment is the relocation address */
-	movq	%rbx, %rdi
-	call	.Ladjust_got
-
 /*
  * Copy the compressed kernel to the end of our buffer
  * where decompression in place becomes safe.
@@ -556,27 +520,6 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
 	jmp	*%rax
 SYM_FUNC_END(.Lrelocated)
 
-/*
- * Adjust the global offset table
- *
- * RAX is the previous adjustment of the table to undo (use 0 if it's the
- * first time we touch GOT).
- * RDI is the new adjustment to apply.
- */
-.Ladjust_got:
-	/* Walk through the GOT adding the address to the entries */
-	leaq	_got(%rip), %rdx
-	leaq	_egot(%rip), %rcx
-1:
-	cmpq	%rcx, %rdx
-	jae	2f
-	subq	%rax, (%rdx)	/* Undo previous adjustment */
-	addq	%rdi, (%rdx)	/* Apply the new adjustment */
-	addq	$8, %rdx
-	jmp	1b
-2:
-	ret
-
 	.code32
 /*
  * This is the 32-bit trampoline that will be copied over to low memory.
diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 4bcc943..a4a4a59 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -43,9 +43,7 @@ SECTIONS
 		_erodata = . ;
 	}
 	.got : {
-		_got = .;
-		KEEP(*(.got))
-		_egot = .;
+		*(.got)
 	}
 	.got.plt : {
 		*(.got.plt)

  reply index

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-31 23:07 [PATCH v5 00/36] Warn on orphan section placement Kees Cook
2020-07-31 23:07 ` [PATCH v5 01/36] x86/boot/compressed: Move .got.plt entries out of the .got section Kees Cook
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Ard Biesheuvel
2020-07-31 23:07 ` [PATCH v5 02/36] x86/boot/compressed: Force hidden visibility for all symbol references Kees Cook
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Ard Biesheuvel
2020-07-31 23:07 ` [PATCH v5 03/36] x86/boot/compressed: Get rid of GOT fixup code Kees Cook
2020-08-14 15:23   ` tip-bot2 for Ard Biesheuvel [this message]
2020-07-31 23:07 ` [PATCH v5 04/36] x86/boot: Add .text.* to setup.ld Kees Cook
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-07-31 23:07 ` [PATCH v5 05/36] x86/boot: Remove run-time relocations from .head.text code Kees Cook
2020-07-31 23:42   ` Nick Desaulniers
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-07-31 23:07 ` [PATCH v5 06/36] x86/boot: Remove run-time relocations from head_{32,64}.S Kees Cook
2020-08-07 18:12   ` Nick Desaulniers
2020-08-07 20:20     ` Arvind Sankar
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-07-31 23:07 ` [PATCH v5 07/36] x86/boot: Check that there are no run-time relocations Kees Cook
2020-08-14 15:23   ` [tip: x86/boot] " tip-bot2 for Arvind Sankar
2020-07-31 23:07 ` [PATCH v5 08/36] vmlinux.lds.h: Create COMMON_DISCARDS Kees Cook
2020-07-31 23:07 ` [PATCH v5 09/36] vmlinux.lds.h: Add .gnu.version* to COMMON_DISCARDS Kees Cook
2020-07-31 23:07 ` [PATCH v5 10/36] vmlinux.lds.h: Avoid KASAN and KCSAN's unwanted sections Kees Cook
2020-07-31 23:07 ` [PATCH v5 11/36] vmlinux.lds.h: Split ELF_DETAILS from STABS_DEBUG Kees Cook
2020-07-31 23:07 ` [PATCH v5 12/36] vmlinux.lds.h: Add .symtab, .strtab, and .shstrtab to ELF_DETAILS Kees Cook
2020-07-31 23:07 ` [PATCH v5 13/36] vmlinux.lds.h: add PGO and AutoFDO input sections Kees Cook
2020-08-01  3:51   ` Arvind Sankar
2020-08-01  6:18     ` Kees Cook
2020-08-01 17:27       ` Arvind Sankar
2020-08-03 19:05     ` Andi Kleen
2020-08-03 20:15       ` Arvind Sankar
2020-08-04  1:19         ` Fāng-ruì Sòng
2020-08-04  4:45         ` Andi Kleen
2020-08-04  5:32           ` Fāng-ruì Sòng
2020-08-04 16:06           ` Arvind Sankar
2020-08-21 19:18             ` Kees Cook
2020-07-31 23:07 ` [PATCH v5 14/36] efi/libstub: Disable -mbranch-protection Kees Cook
2020-07-31 23:07 ` [PATCH v5 15/36] arm64/mm: Remove needless section quotes Kees Cook
2020-07-31 23:08 ` [PATCH v5 16/36] arm64/kernel: Remove needless Call Frame Information annotations Kees Cook
2020-07-31 23:08 ` [PATCH v5 17/36] arm64/build: Remove .eh_frame* sections due to unwind tables Kees Cook
2020-07-31 23:08 ` [PATCH v5 18/36] arm64/build: Use common DISCARDS in linker script Kees Cook
2020-07-31 23:08 ` [PATCH v5 19/36] arm64/build: Add missing DWARF sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 20/36] arm64/build: Assert for unwanted sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 21/36] arm64/build: Warn on orphan section placement Kees Cook
2020-07-31 23:08 ` [PATCH v5 22/36] arm/build: Refactor linker script headers Kees Cook
2020-07-31 23:08 ` [PATCH v5 23/36] arm/build: Explicitly keep .ARM.attributes sections Kees Cook
2020-08-03 19:02   ` Nick Desaulniers
2020-08-17 22:06     ` Fangrui Song
2020-07-31 23:08 ` [PATCH v5 24/36] arm/build: Add missing sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 25/36] arm/build: Warn on orphan section placement Kees Cook
2020-07-31 23:08 ` [PATCH v5 26/36] arm/boot: Handle all sections explicitly Kees Cook
2020-07-31 23:08 ` [PATCH v5 27/36] arm/boot: Warn on orphan section placement Kees Cook
2020-07-31 23:08 ` [PATCH v5 28/36] x86/asm: Avoid generating unused kprobe sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 29/36] x86/build: Enforce an empty .got.plt section Kees Cook
2020-08-01  2:12   ` Arvind Sankar
2020-08-01  5:32     ` Kees Cook
2020-08-21 17:49     ` Kees Cook
2020-07-31 23:08 ` [PATCH v5 30/36] x86/build: Assert for unwanted sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 31/36] x86/build: Warn on orphan section placement Kees Cook
2020-07-31 23:08 ` [PATCH v5 32/36] x86/boot/compressed: Reorganize zero-size section asserts Kees Cook
2020-08-01  1:47   ` Arvind Sankar
2020-08-01  2:53     ` Arvind Sankar
2020-08-01  5:36       ` Kees Cook
2020-08-01 17:12         ` Arvind Sankar
2020-08-21 18:24           ` Kees Cook
2020-08-01  5:35     ` Kees Cook
2020-08-01 17:00       ` Arvind Sankar
2020-08-21 18:19     ` Kees Cook
2020-07-31 23:08 ` [PATCH v5 33/36] x86/boot/compressed: Remove, discard, or assert for unwanted sections Kees Cook
2020-07-31 23:08 ` [PATCH v5 34/36] x86/boot/compressed: Add missing debugging sections to output Kees Cook
2020-07-31 23:08 ` [PATCH v5 35/36] x86/boot/compressed: Warn on orphan section placement Kees Cook
2020-07-31 23:08 ` [PATCH v5 36/36] arm/build: Assert for unwanted sections Kees Cook

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