160 lines
6.0 KiB
Diff
160 lines
6.0 KiB
Diff
From 6d92bc9d483aa1751755a66fee8fb39dffb088c0 Mon Sep 17 00:00:00 2001
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From: "H.J. Lu" <hjl.tools@gmail.com>
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Date: Wed, 16 Mar 2016 20:04:35 -0700
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Subject: [PATCH] x86/build: Build compressed x86 kernels as PIE
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The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X
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relocation to get the symbol address in PIC. When the compressed x86
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kernel isn't built as PIC, the linker optimizes R_386_GOT32X relocations
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to their fixed symbol addresses. However, when the compressed x86
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kernel is loaded at a different address, it leads to the following
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load failure:
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Failed to allocate space for phdrs
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during the decompression stage.
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If the compressed x86 kernel is relocatable at run-time, it should be
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compiled with -fPIE, instead of -fPIC, if possible and should be built as
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Position Independent Executable (PIE) so that linker won't optimize
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R_386_GOT32X relocation to its fixed symbol address.
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Older linkers generate R_386_32 relocations against locally defined
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symbols, _bss, _ebss, _got and _egot, in PIE. It isn't wrong, just less
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optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle
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R_386_32 relocations when relocating the kernel. To generate
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R_386_RELATIVE relocations, we mark _bss, _ebss, _got and _egot as
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hidden in both 32-bit and 64-bit x86 kernels.
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To build a 64-bit compressed x86 kernel as PIE, we need to disable the
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relocation overflow check to avoid relocation overflow errors. We do
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this with a new linker command-line option, -z noreloc-overflow, which
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got added recently:
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commit 4c10bbaa0912742322f10d9d5bb630ba4e15dfa7
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Author: H.J. Lu <hjl.tools@gmail.com>
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Date: Tue Mar 15 11:07:06 2016 -0700
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Add -z noreloc-overflow option to x86-64 ld
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Add -z noreloc-overflow command-line option to the x86-64 ELF linker to
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disable relocation overflow check. This can be used to avoid relocation
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overflow check if there will be no dynamic relocation overflow at
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run-time.
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The 64-bit compressed x86 kernel is built as PIE only if the linker supports
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-z noreloc-overflow. So far 64-bit relocatable compressed x86 kernel
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boots fine even when it is built as a normal executable.
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Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
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Cc: Andy Lutomirski <luto@amacapital.net>
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Cc: Borislav Petkov <bp@alien8.de>
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Cc: Brian Gerst <brgerst@gmail.com>
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Cc: Denys Vlasenko <dvlasenk@redhat.com>
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Cc: H. Peter Anvin <hpa@zytor.com>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Thomas Gleixner <tglx@linutronix.de>
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Cc: linux-kernel@vger.kernel.org
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[ Edited the changelog and comments. ]
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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---
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arch/x86/boot/compressed/Makefile | 14 +++++++++++++-
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arch/x86/boot/compressed/head_32.S | 28 ++++++++++++++++++++++++++++
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arch/x86/boot/compressed/head_64.S | 8 ++++++++
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3 files changed, 49 insertions(+), 1 deletion(-)
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diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
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index 6915ff2..8774cb2 100644
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--- a/arch/x86/boot/compressed/Makefile
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+++ b/arch/x86/boot/compressed/Makefile
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@@ -26,7 +26,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
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vmlinux.bin.xz vmlinux.bin.lzo vmlinux.bin.lz4
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KBUILD_CFLAGS := -m$(BITS) -D__KERNEL__ $(LINUX_INCLUDE) -O2
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-KBUILD_CFLAGS += -fno-strict-aliasing -fPIC
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+KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC)
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KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
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cflags-$(CONFIG_X86_32) := -march=i386
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cflags-$(CONFIG_X86_64) := -mcmodel=small
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@@ -40,6 +40,18 @@ GCOV_PROFILE := n
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UBSAN_SANITIZE :=n
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LDFLAGS := -m elf_$(UTS_MACHINE)
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+ifeq ($(CONFIG_RELOCATABLE),y)
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+# If kernel is relocatable, build compressed kernel as PIE.
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+ifeq ($(CONFIG_X86_32),y)
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+LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
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+else
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+# To build 64-bit compressed kernel as PIE, we disable relocation
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+# overflow check to avoid relocation overflow error with a new linker
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+# command-line option, -z noreloc-overflow.
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+LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \
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+ && echo "-z noreloc-overflow -pie --no-dynamic-linker")
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+endif
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+endif
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LDFLAGS_vmlinux := -T
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hostprogs-y := mkpiggy
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diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
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index 8ef964d..0256064 100644
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--- a/arch/x86/boot/compressed/head_32.S
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+++ b/arch/x86/boot/compressed/head_32.S
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@@ -31,6 +31,34 @@
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#include <asm/asm-offsets.h>
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#include <asm/bootparam.h>
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+/*
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+ * The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X
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+ * relocation to get the symbol address in PIC. When the compressed x86
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+ * kernel isn't built as PIC, the linker optimizes R_386_GOT32X
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+ * relocations to their fixed symbol addresses. However, when the
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+ * compressed x86 kernel is loaded at a different address, it leads
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+ * to the following load failure:
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+ *
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+ * Failed to allocate space for phdrs
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+ *
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+ * during the decompression stage.
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+ *
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+ * If the compressed x86 kernel is relocatable at run-time, it should be
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+ * compiled with -fPIE, instead of -fPIC, if possible and should be built as
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+ * Position Independent Executable (PIE) so that linker won't optimize
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+ * R_386_GOT32X relocation to its fixed symbol address. Older
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+ * linkers generate R_386_32 relocations against locally defined symbols,
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+ * _bss, _ebss, _got and _egot, in PIE. It isn't wrong, just less
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+ * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle
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+ * R_386_32 relocations when relocating the kernel. To generate
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+ * R_386_RELATIVE relocations, we mark _bss, _ebss, _got and _egot as
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+ * hidden:
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+ */
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+ .hidden _bss
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+ .hidden _ebss
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+ .hidden _got
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+ .hidden _egot
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+
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__HEAD
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ENTRY(startup_32)
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#ifdef CONFIG_EFI_STUB
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diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
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index b0c0d16..86558a1 100644
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--- a/arch/x86/boot/compressed/head_64.S
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+++ b/arch/x86/boot/compressed/head_64.S
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@@ -33,6 +33,14 @@
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#include <asm/asm-offsets.h>
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#include <asm/bootparam.h>
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+/*
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+ * Locally defined symbols should be marked hidden:
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+ */
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+ .hidden _bss
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+ .hidden _ebss
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+ .hidden _got
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+ .hidden _egot
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+
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__HEAD
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.code32
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ENTRY(startup_32)
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--
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2.7.3
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