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From: Ross Philipson <ross.philipson@oracle.com>
To: linux-kernel@vger.kernel.org, x86@kernel.org,
	iommu@lists.linux-foundation.org,
	linux-integrity@vger.kernel.org, linux-doc@vger.kernel.org
Cc: ross.philipson@oracle.com, dpsmith@apertussolutions.com,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	hpa@zytor.com, luto@amacapital.net,
	trenchboot-devel@googlegroups.com
Subject: [PATCH v2 01/12] x86/boot: Place kernel_info at a fixed offset
Date: Fri, 18 Jun 2021 12:12:46 -0400	[thread overview]
Message-ID: <1624032777-7013-2-git-send-email-ross.philipson@oracle.com> (raw)
In-Reply-To: <1624032777-7013-1-git-send-email-ross.philipson@oracle.com>

From: Arvind Sankar <nivedita@alum.mit.edu>

There are use cases for storing the offset of a symbol in kernel_info.
For example, the trenchboot series [0] needs to store the offset of the
Measured Launch Environment header in kernel_info.

Since commit (note: commit ID from tip/master)

  527afc212231 ("x86/boot: Check that there are no run-time relocations")

run-time relocations are not allowed in the compressed kernel, so simply
using the symbol in kernel_info, as

	.long	symbol

will cause a linker error because this is not position-independent.

With kernel_info being a separate object file and in a different section
from startup_32, there is no way to calculate the offset of a symbol
from the start of the image in a position-independent way.

To enable such use cases, put kernel_info into its own section which is
placed at a predetermined offset (KERNEL_INFO_OFFSET) via the linker
script. This will allow calculating the symbol offset in a
position-independent way, by adding the offset from the start of
kernel_info to KERNEL_INFO_OFFSET.

Ensure that kernel_info is aligned, and use the SYM_DATA.* macros
instead of bare labels. This stores the size of the kernel_info
structure in the ELF symbol table.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Ross Philipson <ross.philipson@oracle.com>
Signed-off-by: Ross Philipson <ross.philipson@oracle.com>
---
 arch/x86/boot/compressed/kernel_info.S | 19 +++++++++++++++----
 arch/x86/boot/compressed/kernel_info.h | 12 ++++++++++++
 arch/x86/boot/compressed/vmlinux.lds.S |  6 ++++++
 3 files changed, 33 insertions(+), 4 deletions(-)
 create mode 100644 arch/x86/boot/compressed/kernel_info.h

diff --git a/arch/x86/boot/compressed/kernel_info.S b/arch/x86/boot/compressed/kernel_info.S
index f818ee8..c18f071 100644
--- a/arch/x86/boot/compressed/kernel_info.S
+++ b/arch/x86/boot/compressed/kernel_info.S
@@ -1,12 +1,23 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 
+#include <linux/linkage.h>
 #include <asm/bootparam.h>
+#include "kernel_info.h"
 
-	.section ".rodata.kernel_info", "a"
+/*
+ * If a field needs to hold the offset of a symbol from the start
+ * of the image, use the macro below, eg
+ *	.long	rva(symbol)
+ * This will avoid creating run-time relocations, which are not
+ * allowed in the compressed kernel.
+ */
+
+#define rva(X) (((X) - kernel_info) + KERNEL_INFO_OFFSET)
 
-	.global kernel_info
+	.section ".rodata.kernel_info", "a"
 
-kernel_info:
+	.balign	16
+SYM_DATA_START(kernel_info)
 	/* Header, Linux top (structure). */
 	.ascii	"LToP"
 	/* Size. */
@@ -19,4 +30,4 @@ kernel_info:
 
 kernel_info_var_len_data:
 	/* Empty for time being... */
-kernel_info_end:
+SYM_DATA_END_LABEL(kernel_info, SYM_L_LOCAL, kernel_info_end)
diff --git a/arch/x86/boot/compressed/kernel_info.h b/arch/x86/boot/compressed/kernel_info.h
new file mode 100644
index 00000000..c127f84
--- /dev/null
+++ b/arch/x86/boot/compressed/kernel_info.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef BOOT_COMPRESSED_KERNEL_INFO_H
+#define BOOT_COMPRESSED_KERNEL_INFO_H
+
+#ifdef CONFIG_X86_64
+#define KERNEL_INFO_OFFSET 0x500
+#else /* 32-bit */
+#define KERNEL_INFO_OFFSET 0x100
+#endif
+
+#endif /* BOOT_COMPRESSED_KERNEL_INFO_H */
diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 112b237..84c7b4d 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -7,6 +7,7 @@ OUTPUT_FORMAT(CONFIG_OUTPUT_FORMAT)
 
 #include <asm/cache.h>
 #include <asm/page_types.h>
+#include "kernel_info.h"
 
 #ifdef CONFIG_X86_64
 OUTPUT_ARCH(i386:x86-64)
@@ -27,6 +28,11 @@ SECTIONS
 		HEAD_TEXT
 		_ehead = . ;
 	}
+	.rodata.kernel_info KERNEL_INFO_OFFSET : {
+		*(.rodata.kernel_info)
+	}
+	ASSERT(ABSOLUTE(kernel_info) == KERNEL_INFO_OFFSET, "kernel_info at bad address!")
+
 	.rodata..compressed : {
 		*(.rodata..compressed)
 	}
-- 
1.8.3.1


  reply	other threads:[~2021-06-18 16:08 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-18 16:12 [PATCH v2 00/12] x86: Trenchboot secure dynamic launch Linux kernel support Ross Philipson
2021-06-18 16:12 ` Ross Philipson [this message]
2021-06-18 16:12 ` [PATCH v2 02/12] x86: Secure Launch Kconfig Ross Philipson
2021-06-18 16:12 ` [PATCH v2 03/12] x86: Secure Launch main header file Ross Philipson
2021-06-18 16:12 ` [PATCH v2 04/12] x86: Add early SHA support for Secure Launch early measurements Ross Philipson
2021-06-18 16:12 ` [PATCH v2 05/12] x86: Secure Launch kernel early boot stub Ross Philipson
2021-06-18 16:12 ` [PATCH v2 06/12] x86: Secure Launch kernel late " Ross Philipson
2021-06-18 16:12 ` [PATCH v2 07/12] x86: Secure Launch SMP bringup support Ross Philipson
2021-06-18 16:12 ` [PATCH v2 08/12] kexec: Secure Launch kexec SEXIT support Ross Philipson
2021-06-18 16:12 ` [PATCH v2 09/12] reboot: Secure Launch SEXIT support on reboot paths Ross Philipson
2021-06-18 16:12 ` [PATCH v2 10/12] x86: Secure Launch late initcall platform module Ross Philipson
2021-06-18 16:12 ` [PATCH v2 11/12] tpm: Allow locality 2 to be set when initializing the TPM for Secure Launch Ross Philipson
2021-06-18 16:12 ` [PATCH v2 12/12] iommu: Do not allow IOMMU passthrough with " Ross Philipson
2021-06-18 18:32   ` Robin Murphy
2021-06-21 17:51     ` Ross Philipson
2021-06-21 21:15       ` Andy Lutomirski
2021-06-30  9:50         ` Ross Philipson
2021-08-04  3:05         ` Daniel P. Smith
2021-06-22 11:06       ` Robin Murphy
2021-06-30  9:47         ` Ross Philipson

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