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* [PATCH v8 0/3] Introduce 64b relocatable kernel
@ 2023-02-15 14:36 Alexandre Ghiti
  2023-02-15 14:36 ` [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE Alexandre Ghiti
                   ` (3 more replies)
  0 siblings, 4 replies; 19+ messages in thread
From: Alexandre Ghiti @ 2023-02-15 14:36 UTC (permalink / raw)
  To: Michael Ellerman, Nicholas Piggin, Christophe Leroy,
	Paul Walmsley, Palmer Dabbelt, Albert Ou, linuxppc-dev,
	linux-kernel, linux-riscv
  Cc: Alexandre Ghiti

After multiple attempts, this patchset is now based on the fact that the
64b kernel mapping was moved outside the linear mapping.

The first patch allows to build relocatable kernels but is not selected
by default. That patch is a requirement for KASLR.
The second and third patches take advantage of an already existing powerpc
script that checks relocations at compile-time, and uses it for riscv.

This patchset is rebased on top of:

RISC-V kasan rework (https://lore.kernel.org/lkml/Y6TTvku%2FyuSjm42j@spud/T/)
riscv: Use PUD/P4D/PGD pages for the linear mapping (https://lore.kernel.org/lkml/20230125114229.hrhsyw4aegrnmoau@orel/T/)
riscv: Allow to downgrade paging mode from the command line (https://lore.kernel.org/lkml/CAHVXubjeSMvfTPnvrnYRupOGx6+vUvUGfRS3piTeo=TH2cHKNg@mail.gmail.com/)
base-commit-tag: v6.2-rc7

Changes in v8:
  * Fix UEFI boot by moving rela.dyn section into the data so that PE/COFF
    loader actually copies the relocations too
  * Fix check that used PGDIR instead of PUD which was not correct
    for sv48 and sv57
  * Fix PE/COFF header data size definition as it led to size of 0

Changes in v7:
  * Rebase on top of v5.15
  * Fix LDFLAGS_vmlinux which was overriden when CONFIG_DYNAMIC_FTRACE was
    set
  * Make relocate_kernel static
  * Add Ack from Michael

Changes in v6:
  * Remove the kernel move to vmalloc zone
  * Rebased on top of for-next
  * Remove relocatable property from 32b kernel as the kernel is mapped in
    the linear mapping and would then need to be copied physically too
  * CONFIG_RELOCATABLE depends on !XIP_KERNEL
  * Remove Reviewed-by from first patch as it changed a bit

Changes in v5:
  * Add "static __init" to create_kernel_page_table function as reported by
    Kbuild test robot
  * Add reviewed-by from Zong
  * Rebase onto v5.7

Changes in v4:
  * Fix BPF region that overlapped with kernel's as suggested by Zong
  * Fix end of module region that could be larger than 2GB as suggested by Zong
  * Fix the size of the vm area reserved for the kernel as we could lose
    PMD_SIZE if the size was already aligned on PMD_SIZE
  * Split compile time relocations check patch into 2 patches as suggested by Anup
  * Applied Reviewed-by from Zong and Anup

Changes in v3:
  * Move kernel mapping to vmalloc

Changes in v2:
  * Make RELOCATABLE depend on MMU as suggested by Anup
  * Rename kernel_load_addr into kernel_virt_addr as suggested by Anup
  * Use __pa_symbol instead of __pa, as suggested by Zong
  * Rebased on top of v5.6-rc3
  * Tested with sv48 patchset
  * Add Reviewed/Tested-by from Zong and Anup

Alexandre Ghiti (3):
  riscv: Introduce CONFIG_RELOCATABLE
  powerpc: Move script to check relocations at compile time in scripts/
  riscv: Check relocations at compile time

 arch/powerpc/tools/relocs_check.sh | 18 ++--------
 arch/riscv/Kconfig                 | 14 ++++++++
 arch/riscv/Makefile                |  7 ++--
 arch/riscv/Makefile.postlink       | 36 ++++++++++++++++++++
 arch/riscv/kernel/efi-header.S     |  6 ++--
 arch/riscv/kernel/vmlinux.lds.S    | 10 ++++--
 arch/riscv/mm/Makefile             |  4 +++
 arch/riscv/mm/init.c               | 54 +++++++++++++++++++++++++++++-
 arch/riscv/tools/relocs_check.sh   | 26 ++++++++++++++
 scripts/relocs_check.sh            | 20 +++++++++++
 10 files changed, 171 insertions(+), 24 deletions(-)
 create mode 100644 arch/riscv/Makefile.postlink
 create mode 100755 arch/riscv/tools/relocs_check.sh
 create mode 100755 scripts/relocs_check.sh

--
2.37.2


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^ permalink raw reply	[flat|nested] 19+ messages in thread

* [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-02-15 14:36 [PATCH v8 0/3] Introduce 64b relocatable kernel Alexandre Ghiti
@ 2023-02-15 14:36 ` Alexandre Ghiti
  2023-02-22 12:29   ` Alexandre Ghiti
  2023-05-09 19:07   ` Andreas Schwab
  2023-02-15 14:36 ` [PATCH v8 2/3] powerpc: Move script to check relocations at compile time in scripts/ Alexandre Ghiti
                   ` (2 subsequent siblings)
  3 siblings, 2 replies; 19+ messages in thread
From: Alexandre Ghiti @ 2023-02-15 14:36 UTC (permalink / raw)
  To: Michael Ellerman, Nicholas Piggin, Christophe Leroy,
	Paul Walmsley, Palmer Dabbelt, Albert Ou, linuxppc-dev,
	linux-kernel, linux-riscv
  Cc: Alexandre Ghiti

From: Alexandre Ghiti <alex@ghiti.fr>

This config allows to compile 64b kernel as PIE and to relocate it at
any virtual address at runtime: this paves the way to KASLR.
Runtime relocation is possible since relocation metadata are embedded into
the kernel.

Note that relocating at runtime introduces an overhead even if the
kernel is loaded at the same address it was linked at and that the compiler
options are those used in arm64 which uses the same RELA relocation
format.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
---
 arch/riscv/Kconfig              | 14 +++++++++
 arch/riscv/Makefile             |  7 +++--
 arch/riscv/kernel/efi-header.S  |  6 ++--
 arch/riscv/kernel/vmlinux.lds.S | 10 ++++--
 arch/riscv/mm/Makefile          |  4 +++
 arch/riscv/mm/init.c            | 54 ++++++++++++++++++++++++++++++++-
 6 files changed, 87 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index e2b656043abf..e0ee7ce4b2e3 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -544,6 +544,20 @@ config COMPAT
 
 	  If you want to execute 32-bit userspace applications, say Y.
 
+config RELOCATABLE
+	bool "Build a relocatable kernel"
+	depends on MMU && 64BIT && !XIP_KERNEL
+	help
+          This builds a kernel as a Position Independent Executable (PIE),
+          which retains all relocation metadata required to relocate the
+          kernel binary at runtime to a different virtual address than the
+          address it was linked at.
+          Since RISCV uses the RELA relocation format, this requires a
+          relocation pass at runtime even if the kernel is loaded at the
+          same address it was linked at.
+
+          If unsure, say N.
+
 endmenu # "Kernel features"
 
 menu "Boot options"
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 82153960ac00..97c34136b027 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -7,9 +7,12 @@
 #
 
 OBJCOPYFLAGS    := -O binary
-LDFLAGS_vmlinux :=
+ifeq ($(CONFIG_RELOCATABLE),y)
+	LDFLAGS_vmlinux += -shared -Bsymbolic -z notext -z norelro
+	KBUILD_CFLAGS += -fPIE
+endif
 ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
-	LDFLAGS_vmlinux := --no-relax
+	LDFLAGS_vmlinux += --no-relax
 	KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
 	CC_FLAGS_FTRACE := -fpatchable-function-entry=8
 endif
diff --git a/arch/riscv/kernel/efi-header.S b/arch/riscv/kernel/efi-header.S
index 8e733aa48ba6..f7ee09c4f12d 100644
--- a/arch/riscv/kernel/efi-header.S
+++ b/arch/riscv/kernel/efi-header.S
@@ -33,7 +33,7 @@ optional_header:
 	.byte	0x02					// MajorLinkerVersion
 	.byte	0x14					// MinorLinkerVersion
 	.long	__pecoff_text_end - efi_header_end	// SizeOfCode
-	.long	__pecoff_data_virt_size			// SizeOfInitializedData
+	.long	__pecoff_data_virt_end - __pecoff_text_end	// SizeOfInitializedData
 	.long	0					// SizeOfUninitializedData
 	.long	__efistub_efi_pe_entry - _start		// AddressOfEntryPoint
 	.long	efi_header_end - _start			// BaseOfCode
@@ -91,9 +91,9 @@ section_table:
 		IMAGE_SCN_MEM_EXECUTE			// Characteristics
 
 	.ascii	".data\0\0\0"
-	.long	__pecoff_data_virt_size			// VirtualSize
+	.long	__pecoff_data_virt_end - __pecoff_text_end	// VirtualSize
 	.long	__pecoff_text_end - _start		// VirtualAddress
-	.long	__pecoff_data_raw_size			// SizeOfRawData
+	.long	__pecoff_data_raw_end - __pecoff_text_end	// SizeOfRawData
 	.long	__pecoff_text_end - _start		// PointerToRawData
 
 	.long	0					// PointerToRelocations
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 4e6c88aa4d87..8be2de3be08c 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -122,9 +122,15 @@ SECTIONS
 		*(.sdata*)
 	}
 
+	.rela.dyn : ALIGN(8) {
+		__rela_dyn_start = .;
+		*(.rela .rela*)
+		__rela_dyn_end = .;
+	}
+
 #ifdef CONFIG_EFI
 	.pecoff_edata_padding : { BYTE(0); . = ALIGN(PECOFF_FILE_ALIGNMENT); }
-	__pecoff_data_raw_size = ABSOLUTE(. - __pecoff_text_end);
+	__pecoff_data_raw_end = ABSOLUTE(.);
 #endif
 
 	/* End of data section */
@@ -134,7 +140,7 @@ SECTIONS
 
 #ifdef CONFIG_EFI
 	. = ALIGN(PECOFF_SECTION_ALIGNMENT);
-	__pecoff_data_virt_size = ABSOLUTE(. - __pecoff_text_end);
+	__pecoff_data_virt_end = ABSOLUTE(.);
 #endif
 	_end = .;
 
diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
index 2ac177c05352..b85e9e82f082 100644
--- a/arch/riscv/mm/Makefile
+++ b/arch/riscv/mm/Makefile
@@ -1,6 +1,10 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
 CFLAGS_init.o := -mcmodel=medany
+ifdef CONFIG_RELOCATABLE
+CFLAGS_init.o += -fno-pie
+endif
+
 ifdef CONFIG_FTRACE
 CFLAGS_REMOVE_init.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_cacheflush.o = $(CC_FLAGS_FTRACE)
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 7f01c2e56efe..3862696c2ac9 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -20,6 +20,9 @@
 #include <linux/dma-map-ops.h>
 #include <linux/crash_dump.h>
 #include <linux/hugetlb.h>
+#ifdef CONFIG_RELOCATABLE
+#include <linux/elf.h>
+#endif
 
 #include <asm/fixmap.h>
 #include <asm/tlbflush.h>
@@ -146,7 +149,7 @@ static void __init print_vm_layout(void)
 		print_ml("kasan", KASAN_SHADOW_START, KASAN_SHADOW_END);
 #endif
 
-		print_ml("kernel", (unsigned long)KERNEL_LINK_ADDR,
+		print_ml("kernel", (unsigned long)kernel_map.virt_addr,
 			 (unsigned long)ADDRESS_SPACE_END);
 	}
 }
@@ -854,6 +857,44 @@ static __init void set_satp_mode(uintptr_t dtb_pa)
 #error "setup_vm() is called from head.S before relocate so it should not use absolute addressing."
 #endif
 
+#ifdef CONFIG_RELOCATABLE
+extern unsigned long __rela_dyn_start, __rela_dyn_end;
+
+static void __init relocate_kernel(void)
+{
+	Elf64_Rela *rela = (Elf64_Rela *)&__rela_dyn_start;
+	/*
+	 * This holds the offset between the linked virtual address and the
+	 * relocated virtual address.
+	 */
+	uintptr_t reloc_offset = kernel_map.virt_addr - KERNEL_LINK_ADDR;
+	/*
+	 * This holds the offset between kernel linked virtual address and
+	 * physical address.
+	 */
+	uintptr_t va_kernel_link_pa_offset = KERNEL_LINK_ADDR - kernel_map.phys_addr;
+
+	for ( ; rela < (Elf64_Rela *)&__rela_dyn_end; rela++) {
+		Elf64_Addr addr = (rela->r_offset - va_kernel_link_pa_offset);
+		Elf64_Addr relocated_addr = rela->r_addend;
+
+		if (rela->r_info != R_RISCV_RELATIVE)
+			continue;
+
+		/*
+		 * Make sure to not relocate vdso symbols like rt_sigreturn
+		 * which are linked from the address 0 in vmlinux since
+		 * vdso symbol addresses are actually used as an offset from
+		 * mm->context.vdso in VDSO_OFFSET macro.
+		 */
+		if (relocated_addr >= KERNEL_LINK_ADDR)
+			relocated_addr += reloc_offset;
+
+		*(Elf64_Addr *)addr = relocated_addr;
+	}
+}
+#endif /* CONFIG_RELOCATABLE */
+
 #ifdef CONFIG_XIP_KERNEL
 static void __init create_kernel_page_table(pgd_t *pgdir,
 					    __always_unused bool early)
@@ -1039,6 +1080,17 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	BUG_ON((kernel_map.virt_addr + kernel_map.size) > ADDRESS_SPACE_END - SZ_4K);
 #endif
 
+#ifdef CONFIG_RELOCATABLE
+	/*
+	 * Early page table uses only one PUD, which makes it possible
+	 * to map PUD_SIZE aligned on PUD_SIZE: if the relocation offset
+	 * makes the kernel cross over a PUD_SIZE boundary, raise a bug
+	 * since a part of the kernel would not get mapped.
+	 */
+	BUG_ON(PUD_SIZE - (kernel_map.virt_addr & (PUD_SIZE - 1)) < kernel_map.size);
+	relocate_kernel();
+#endif
+
 	apply_early_boot_alternatives();
 	pt_ops_set_early();
 
-- 
2.37.2


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^ permalink raw reply related	[flat|nested] 19+ messages in thread

* [PATCH v8 2/3] powerpc: Move script to check relocations at compile time in scripts/
  2023-02-15 14:36 [PATCH v8 0/3] Introduce 64b relocatable kernel Alexandre Ghiti
  2023-02-15 14:36 ` [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE Alexandre Ghiti
@ 2023-02-15 14:36 ` Alexandre Ghiti
  2023-02-15 14:36 ` [PATCH v8 3/3] riscv: Check relocations at compile time Alexandre Ghiti
  2023-02-20  9:14 ` [PATCH v8 0/3] Introduce 64b relocatable kernel Björn Töpel
  3 siblings, 0 replies; 19+ messages in thread
From: Alexandre Ghiti @ 2023-02-15 14:36 UTC (permalink / raw)
  To: Michael Ellerman, Nicholas Piggin, Christophe Leroy,
	Paul Walmsley, Palmer Dabbelt, Albert Ou, linuxppc-dev,
	linux-kernel, linux-riscv
  Cc: Alexandre Ghiti, Anup Patel

From: Alexandre Ghiti <alex@ghiti.fr>

Relocating kernel at runtime is done very early in the boot process, so
it is not convenient to check for relocations there and react in case a
relocation was not expected.

Powerpc architecture has a script that allows to check at compile time
for such unexpected relocations: extract the common logic to scripts/
so that other architectures can take advantage of it.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Reviewed-by: Anup Patel <anup@brainfault.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
---
 arch/powerpc/tools/relocs_check.sh | 18 ++----------------
 scripts/relocs_check.sh            | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+), 16 deletions(-)
 create mode 100755 scripts/relocs_check.sh

diff --git a/arch/powerpc/tools/relocs_check.sh b/arch/powerpc/tools/relocs_check.sh
index 63792af00417..6b350e75014c 100755
--- a/arch/powerpc/tools/relocs_check.sh
+++ b/arch/powerpc/tools/relocs_check.sh
@@ -15,21 +15,8 @@ if [ $# -lt 3 ]; then
 	exit 1
 fi
 
-# Have Kbuild supply the path to objdump and nm so we handle cross compilation.
-objdump="$1"
-nm="$2"
-vmlinux="$3"
-
-# Remove from the bad relocations those that match an undefined weak symbol
-# which will result in an absolute relocation to 0.
-# Weak unresolved symbols are of that form in nm output:
-# "                  w _binary__btf_vmlinux_bin_end"
-undef_weak_symbols=$($nm "$vmlinux" | awk '$1 ~ /w/ { print $2 }')
-
 bad_relocs=$(
-$objdump -R "$vmlinux" |
-	# Only look at relocation lines.
-	grep -E '\<R_' |
+${srctree}/scripts/relocs_check.sh "$@" |
 	# These relocations are okay
 	# On PPC64:
 	#	R_PPC64_RELATIVE, R_PPC64_NONE
@@ -44,8 +31,7 @@ R_PPC_ADDR16_LO
 R_PPC_ADDR16_HI
 R_PPC_ADDR16_HA
 R_PPC_RELATIVE
-R_PPC_NONE' |
-	([ "$undef_weak_symbols" ] && grep -F -w -v "$undef_weak_symbols" || cat)
+R_PPC_NONE'
 )
 
 if [ -z "$bad_relocs" ]; then
diff --git a/scripts/relocs_check.sh b/scripts/relocs_check.sh
new file mode 100755
index 000000000000..137c660499f3
--- /dev/null
+++ b/scripts/relocs_check.sh
@@ -0,0 +1,20 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+# Get a list of all the relocations, remove from it the relocations
+# that are known to be legitimate and return this list to arch specific
+# script that will look for suspicious relocations.
+
+objdump="$1"
+nm="$2"
+vmlinux="$3"
+
+# Remove from the possible bad relocations those that match an undefined
+# weak symbol which will result in an absolute relocation to 0.
+# Weak unresolved symbols are of that form in nm output:
+# "                  w _binary__btf_vmlinux_bin_end"
+undef_weak_symbols=$($nm "$vmlinux" | awk '$1 ~ /w/ { print $2 }')
+
+$objdump -R "$vmlinux" |
+	grep -E '\<R_' |
+	([ "$undef_weak_symbols" ] && grep -F -w -v "$undef_weak_symbols" || cat)
-- 
2.37.2


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http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply related	[flat|nested] 19+ messages in thread

* [PATCH v8 3/3] riscv: Check relocations at compile time
  2023-02-15 14:36 [PATCH v8 0/3] Introduce 64b relocatable kernel Alexandre Ghiti
  2023-02-15 14:36 ` [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE Alexandre Ghiti
  2023-02-15 14:36 ` [PATCH v8 2/3] powerpc: Move script to check relocations at compile time in scripts/ Alexandre Ghiti
@ 2023-02-15 14:36 ` Alexandre Ghiti
  2023-02-20  9:14 ` [PATCH v8 0/3] Introduce 64b relocatable kernel Björn Töpel
  3 siblings, 0 replies; 19+ messages in thread
From: Alexandre Ghiti @ 2023-02-15 14:36 UTC (permalink / raw)
  To: Michael Ellerman, Nicholas Piggin, Christophe Leroy,
	Paul Walmsley, Palmer Dabbelt, Albert Ou, linuxppc-dev,
	linux-kernel, linux-riscv
  Cc: Alexandre Ghiti, Anup Patel

From: Alexandre Ghiti <alex@ghiti.fr>

Relocating kernel at runtime is done very early in the boot process, so
it is not convenient to check for relocations there and react in case a
relocation was not expected.

There exists a script in scripts/ that extracts the relocations from
vmlinux that is then used at postlink to check the relocations.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Reviewed-by: Anup Patel <anup@brainfault.org>
---
 arch/riscv/Makefile.postlink     | 36 ++++++++++++++++++++++++++++++++
 arch/riscv/tools/relocs_check.sh | 26 +++++++++++++++++++++++
 2 files changed, 62 insertions(+)
 create mode 100644 arch/riscv/Makefile.postlink
 create mode 100755 arch/riscv/tools/relocs_check.sh

diff --git a/arch/riscv/Makefile.postlink b/arch/riscv/Makefile.postlink
new file mode 100644
index 000000000000..bf2b2bca1845
--- /dev/null
+++ b/arch/riscv/Makefile.postlink
@@ -0,0 +1,36 @@
+# SPDX-License-Identifier: GPL-2.0
+# ===========================================================================
+# Post-link riscv pass
+# ===========================================================================
+#
+# Check that vmlinux relocations look sane
+
+PHONY := __archpost
+__archpost:
+
+-include include/config/auto.conf
+include scripts/Kbuild.include
+
+quiet_cmd_relocs_check = CHKREL  $@
+cmd_relocs_check = 							\
+	$(CONFIG_SHELL) $(srctree)/arch/riscv/tools/relocs_check.sh "$(OBJDUMP)" "$(NM)" "$@"
+
+# `@true` prevents complaint when there is nothing to be done
+
+vmlinux: FORCE
+	@true
+ifdef CONFIG_RELOCATABLE
+	$(call if_changed,relocs_check)
+endif
+
+%.ko: FORCE
+	@true
+
+clean:
+	@true
+
+PHONY += FORCE clean
+
+FORCE:
+
+.PHONY: $(PHONY)
diff --git a/arch/riscv/tools/relocs_check.sh b/arch/riscv/tools/relocs_check.sh
new file mode 100755
index 000000000000..baeb2e7b2290
--- /dev/null
+++ b/arch/riscv/tools/relocs_check.sh
@@ -0,0 +1,26 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Based on powerpc relocs_check.sh
+
+# This script checks the relocations of a vmlinux for "suspicious"
+# relocations.
+
+if [ $# -lt 3 ]; then
+        echo "$0 [path to objdump] [path to nm] [path to vmlinux]" 1>&2
+        exit 1
+fi
+
+bad_relocs=$(
+${srctree}/scripts/relocs_check.sh "$@" |
+	# These relocations are okay
+	#	R_RISCV_RELATIVE
+	grep -F -w -v 'R_RISCV_RELATIVE'
+)
+
+if [ -z "$bad_relocs" ]; then
+	exit 0
+fi
+
+num_bad=$(echo "$bad_relocs" | wc -l)
+echo "WARNING: $num_bad bad relocations"
+echo "$bad_relocs"
-- 
2.37.2


_______________________________________________
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linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply related	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 0/3] Introduce 64b relocatable kernel
  2023-02-15 14:36 [PATCH v8 0/3] Introduce 64b relocatable kernel Alexandre Ghiti
                   ` (2 preceding siblings ...)
  2023-02-15 14:36 ` [PATCH v8 3/3] riscv: Check relocations at compile time Alexandre Ghiti
@ 2023-02-20  9:14 ` Björn Töpel
  3 siblings, 0 replies; 19+ messages in thread
From: Björn Töpel @ 2023-02-20  9:14 UTC (permalink / raw)
  To: Alexandre Ghiti, Michael Ellerman, Nicholas Piggin,
	Christophe Leroy, Paul Walmsley, Palmer Dabbelt, Albert Ou,
	linuxppc-dev, linux-kernel, linux-riscv
  Cc: Alexandre Ghiti

Alexandre Ghiti <alexghiti@rivosinc.com> writes:

> After multiple attempts, this patchset is now based on the fact that the
> 64b kernel mapping was moved outside the linear mapping.
>
> The first patch allows to build relocatable kernels but is not selected
> by default. That patch is a requirement for KASLR.
> The second and third patches take advantage of an already existing powerpc
> script that checks relocations at compile-time, and uses it for riscv.
>
> This patchset is rebased on top of:
>
> RISC-V kasan rework (https://lore.kernel.org/lkml/Y6TTvku%2FyuSjm42j@spud/T/)
> riscv: Use PUD/P4D/PGD pages for the linear mapping (https://lore.kernel.org/lkml/20230125114229.hrhsyw4aegrnmoau@orel/T/)
> riscv: Allow to downgrade paging mode from the command line (https://lore.kernel.org/lkml/CAHVXubjeSMvfTPnvrnYRupOGx6+vUvUGfRS3piTeo=TH2cHKNg@mail.gmail.com/)
> base-commit-tag: v6.2-rc7
>
> Changes in v8:
>   * Fix UEFI boot by moving rela.dyn section into the data so that PE/COFF
>     loader actually copies the relocations too
>   * Fix check that used PGDIR instead of PUD which was not correct
>     for sv48 and sv57
>   * Fix PE/COFF header data size definition as it led to size of 0
>
> Changes in v7:
>   * Rebase on top of v5.15
>   * Fix LDFLAGS_vmlinux which was overriden when CONFIG_DYNAMIC_FTRACE was
>     set
>   * Make relocate_kernel static
>   * Add Ack from Michael
>
> Changes in v6:
>   * Remove the kernel move to vmalloc zone
>   * Rebased on top of for-next
>   * Remove relocatable property from 32b kernel as the kernel is mapped in
>     the linear mapping and would then need to be copied physically too
>   * CONFIG_RELOCATABLE depends on !XIP_KERNEL
>   * Remove Reviewed-by from first patch as it changed a bit
>
> Changes in v5:
>   * Add "static __init" to create_kernel_page_table function as reported by
>     Kbuild test robot
>   * Add reviewed-by from Zong
>   * Rebase onto v5.7
>
> Changes in v4:
>   * Fix BPF region that overlapped with kernel's as suggested by Zong
>   * Fix end of module region that could be larger than 2GB as suggested by Zong
>   * Fix the size of the vm area reserved for the kernel as we could lose
>     PMD_SIZE if the size was already aligned on PMD_SIZE
>   * Split compile time relocations check patch into 2 patches as suggested by Anup
>   * Applied Reviewed-by from Zong and Anup
>
> Changes in v3:
>   * Move kernel mapping to vmalloc
>
> Changes in v2:
>   * Make RELOCATABLE depend on MMU as suggested by Anup
>   * Rename kernel_load_addr into kernel_virt_addr as suggested by Anup
>   * Use __pa_symbol instead of __pa, as suggested by Zong
>   * Rebased on top of v5.6-rc3
>   * Tested with sv48 patchset
>   * Add Reviewed/Tested-by from Zong and Anup
>
> Alexandre Ghiti (3):
>   riscv: Introduce CONFIG_RELOCATABLE
>   powerpc: Move script to check relocations at compile time in scripts/
>   riscv: Check relocations at compile time

I'm getting issues booting via UEFI/efi-stub with this, because the PE
header is messed up.

from arch/riscv/kernel/efi-header.S:

 | ...
 | extra_header_fields:
 |         .quad   0                                       // ImageBase
 |         .long   PECOFF_SECTION_ALIGNMENT                // SectionAlignment
 |         .long   PECOFF_FILE_ALIGNMENT                   // FileAlignment
 | ...

PECOFF* is taken from the linker-script, and ends up in relocation
section. When u-boot tried to load the image, alignment is zero and the
loader breaks.


Björn

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^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-02-15 14:36 ` [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE Alexandre Ghiti
@ 2023-02-22 12:29   ` Alexandre Ghiti
  2023-02-24 15:58     ` Björn Töpel
  2023-03-22 13:38     ` Alexandre Ghiti
  2023-05-09 19:07   ` Andreas Schwab
  1 sibling, 2 replies; 19+ messages in thread
From: Alexandre Ghiti @ 2023-02-22 12:29 UTC (permalink / raw)
  To: Alexandre Ghiti, Michael Ellerman, Nicholas Piggin,
	Christophe Leroy, Paul Walmsley, Palmer Dabbelt, Albert Ou,
	linuxppc-dev, linux-kernel, linux-riscv, nathan, linux-kbuild,
	llvm, ndesaulniers, Björn Töpel

+cc linux-kbuild, llvm, Nathan, Nick

On 2/15/23 15:36, Alexandre Ghiti wrote:
> From: Alexandre Ghiti <alex@ghiti.fr>
>
> This config allows to compile 64b kernel as PIE and to relocate it at
> any virtual address at runtime: this paves the way to KASLR.
> Runtime relocation is possible since relocation metadata are embedded into
> the kernel.
>
> Note that relocating at runtime introduces an overhead even if the
> kernel is loaded at the same address it was linked at and that the compiler
> options are those used in arm64 which uses the same RELA relocation
> format.
>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
>   arch/riscv/Kconfig              | 14 +++++++++
>   arch/riscv/Makefile             |  7 +++--
>   arch/riscv/kernel/efi-header.S  |  6 ++--
>   arch/riscv/kernel/vmlinux.lds.S | 10 ++++--
>   arch/riscv/mm/Makefile          |  4 +++
>   arch/riscv/mm/init.c            | 54 ++++++++++++++++++++++++++++++++-
>   6 files changed, 87 insertions(+), 8 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index e2b656043abf..e0ee7ce4b2e3 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -544,6 +544,20 @@ config COMPAT
>   
>   	  If you want to execute 32-bit userspace applications, say Y.
>   
> +config RELOCATABLE
> +	bool "Build a relocatable kernel"
> +	depends on MMU && 64BIT && !XIP_KERNEL
> +	help
> +          This builds a kernel as a Position Independent Executable (PIE),
> +          which retains all relocation metadata required to relocate the
> +          kernel binary at runtime to a different virtual address than the
> +          address it was linked at.
> +          Since RISCV uses the RELA relocation format, this requires a
> +          relocation pass at runtime even if the kernel is loaded at the
> +          same address it was linked at.
> +
> +          If unsure, say N.
> +
>   endmenu # "Kernel features"
>   
>   menu "Boot options"
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 82153960ac00..97c34136b027 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -7,9 +7,12 @@
>   #
>   
>   OBJCOPYFLAGS    := -O binary
> -LDFLAGS_vmlinux :=
> +ifeq ($(CONFIG_RELOCATABLE),y)
> +	LDFLAGS_vmlinux += -shared -Bsymbolic -z notext -z norelro
> +	KBUILD_CFLAGS += -fPIE
> +endif
>   ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
> -	LDFLAGS_vmlinux := --no-relax
> +	LDFLAGS_vmlinux += --no-relax
>   	KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
>   	CC_FLAGS_FTRACE := -fpatchable-function-entry=8
>   endif
> diff --git a/arch/riscv/kernel/efi-header.S b/arch/riscv/kernel/efi-header.S
> index 8e733aa48ba6..f7ee09c4f12d 100644
> --- a/arch/riscv/kernel/efi-header.S
> +++ b/arch/riscv/kernel/efi-header.S
> @@ -33,7 +33,7 @@ optional_header:
>   	.byte	0x02					// MajorLinkerVersion
>   	.byte	0x14					// MinorLinkerVersion
>   	.long	__pecoff_text_end - efi_header_end	// SizeOfCode
> -	.long	__pecoff_data_virt_size			// SizeOfInitializedData
> +	.long	__pecoff_data_virt_end - __pecoff_text_end	// SizeOfInitializedData
>   	.long	0					// SizeOfUninitializedData
>   	.long	__efistub_efi_pe_entry - _start		// AddressOfEntryPoint
>   	.long	efi_header_end - _start			// BaseOfCode
> @@ -91,9 +91,9 @@ section_table:
>   		IMAGE_SCN_MEM_EXECUTE			// Characteristics
>   
>   	.ascii	".data\0\0\0"
> -	.long	__pecoff_data_virt_size			// VirtualSize
> +	.long	__pecoff_data_virt_end - __pecoff_text_end	// VirtualSize
>   	.long	__pecoff_text_end - _start		// VirtualAddress
> -	.long	__pecoff_data_raw_size			// SizeOfRawData
> +	.long	__pecoff_data_raw_end - __pecoff_text_end	// SizeOfRawData
>   	.long	__pecoff_text_end - _start		// PointerToRawData
>   
>   	.long	0					// PointerToRelocations
> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> index 4e6c88aa4d87..8be2de3be08c 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -122,9 +122,15 @@ SECTIONS
>   		*(.sdata*)
>   	}
>   
> +	.rela.dyn : ALIGN(8) {
> +		__rela_dyn_start = .;
> +		*(.rela .rela*)
> +		__rela_dyn_end = .;
> +	}
> +


So I realized those relocations would be better in the init section so 
we can get rid of them at some point. So I tried the following:

diff --git a/arch/riscv/kernel/vmlinux.lds.S 
b/arch/riscv/kernel/vmlinux.lds.S
index 7ac215467fd5..6111023a89ef 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -93,6 +93,12 @@ SECTIONS
                 *(.rel.dyn*)
         }

+       .rela.dyn : ALIGN(8) {
+               __rela_dyn_start = .;
+               *(.rela .rela*)
+               __rela_dyn_end = .;
+       }
+
         __init_data_end = .;

         . = ALIGN(8);
@@ -119,12 +125,6 @@ SECTIONS
                 *(.sdata*)
         }

-       .rela.dyn : ALIGN(8) {
-               __rela_dyn_start = .;
-               *(.rela .rela*)
-               __rela_dyn_end = .;
-       }
-
  #ifdef CONFIG_EFI
         .pecoff_edata_padding : { BYTE(0); . = 
ALIGN(PECOFF_FILE_ALIGNMENT); }
         __pecoff_data_raw_end = ABSOLUTE(.);


But then all the relocations in vmlinux end up being null:

vmlinux:     file format elf64-littleriscv

$ riscv64-linux-gnu-objdump -R vmlinux

DYNAMIC RELOCATION RECORDS
OFFSET           TYPE              VALUE
0000000000000000 R_RISCV_NONE      *ABS*
0000000000000000 R_RISCV_NONE      *ABS*
....

  I also noticed that re-linking vmlinux with the same command right 
after works (ie, the relocations are now valid):

$ riscv64-linux-gnu-objdump -R vmlinux

vmlinux:     file format elf64-littleriscv

DYNAMIC RELOCATION RECORDS
OFFSET           TYPE              VALUE
ffffffff82600718 R_RISCV_RELATIVE  *ABS*-0x000000007d9ff8e8
ffffffff82600720 R_RISCV_RELATIVE  *ABS*-0x000000007d9ff8e8
...

Below is the command used to generate this working vmlinux:

riscv64-unknown-linux-gnu-ld -melf64lriscv -z noexecstack 
--no-warn-rwx-segments -shared -Bsymbolic -z notext -z norelro 
--no-relax --build-id=sha1 --script=./arch/riscv/kernel/vmlinux.lds 
-Map=vmlinux.map -o vmlinux --whole-archive vmlinux.a .vmlinux.export.o 
init/version-timestamp.o --no-whole-archive --start-group 
./drivers/firmware/efi/libstub/lib.a --end-group .tmp_vmlinux.kallsyms3.o

I tried a lot of things, but I struggle to understand, does anyone have 
any idea? FYI, the same problem happens with LLVM.

Thanks,

Alex


>   #ifdef CONFIG_EFI
>   	.pecoff_edata_padding : { BYTE(0); . = ALIGN(PECOFF_FILE_ALIGNMENT); }
> -	__pecoff_data_raw_size = ABSOLUTE(. - __pecoff_text_end);
> +	__pecoff_data_raw_end = ABSOLUTE(.);
>   #endif
>   
>   	/* End of data section */
> @@ -134,7 +140,7 @@ SECTIONS
>   
>   #ifdef CONFIG_EFI
>   	. = ALIGN(PECOFF_SECTION_ALIGNMENT);
> -	__pecoff_data_virt_size = ABSOLUTE(. - __pecoff_text_end);
> +	__pecoff_data_virt_end = ABSOLUTE(.);
>   #endif
>   	_end = .;
>   
> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
> index 2ac177c05352..b85e9e82f082 100644
> --- a/arch/riscv/mm/Makefile
> +++ b/arch/riscv/mm/Makefile
> @@ -1,6 +1,10 @@
>   # SPDX-License-Identifier: GPL-2.0-only
>   
>   CFLAGS_init.o := -mcmodel=medany
> +ifdef CONFIG_RELOCATABLE
> +CFLAGS_init.o += -fno-pie
> +endif
> +
>   ifdef CONFIG_FTRACE
>   CFLAGS_REMOVE_init.o = $(CC_FLAGS_FTRACE)
>   CFLAGS_REMOVE_cacheflush.o = $(CC_FLAGS_FTRACE)
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 7f01c2e56efe..3862696c2ac9 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -20,6 +20,9 @@
>   #include <linux/dma-map-ops.h>
>   #include <linux/crash_dump.h>
>   #include <linux/hugetlb.h>
> +#ifdef CONFIG_RELOCATABLE
> +#include <linux/elf.h>
> +#endif
>   
>   #include <asm/fixmap.h>
>   #include <asm/tlbflush.h>
> @@ -146,7 +149,7 @@ static void __init print_vm_layout(void)
>   		print_ml("kasan", KASAN_SHADOW_START, KASAN_SHADOW_END);
>   #endif
>   
> -		print_ml("kernel", (unsigned long)KERNEL_LINK_ADDR,
> +		print_ml("kernel", (unsigned long)kernel_map.virt_addr,
>   			 (unsigned long)ADDRESS_SPACE_END);
>   	}
>   }
> @@ -854,6 +857,44 @@ static __init void set_satp_mode(uintptr_t dtb_pa)
>   #error "setup_vm() is called from head.S before relocate so it should not use absolute addressing."
>   #endif
>   
> +#ifdef CONFIG_RELOCATABLE
> +extern unsigned long __rela_dyn_start, __rela_dyn_end;
> +
> +static void __init relocate_kernel(void)
> +{
> +	Elf64_Rela *rela = (Elf64_Rela *)&__rela_dyn_start;
> +	/*
> +	 * This holds the offset between the linked virtual address and the
> +	 * relocated virtual address.
> +	 */
> +	uintptr_t reloc_offset = kernel_map.virt_addr - KERNEL_LINK_ADDR;
> +	/*
> +	 * This holds the offset between kernel linked virtual address and
> +	 * physical address.
> +	 */
> +	uintptr_t va_kernel_link_pa_offset = KERNEL_LINK_ADDR - kernel_map.phys_addr;
> +
> +	for ( ; rela < (Elf64_Rela *)&__rela_dyn_end; rela++) {
> +		Elf64_Addr addr = (rela->r_offset - va_kernel_link_pa_offset);
> +		Elf64_Addr relocated_addr = rela->r_addend;
> +
> +		if (rela->r_info != R_RISCV_RELATIVE)
> +			continue;
> +
> +		/*
> +		 * Make sure to not relocate vdso symbols like rt_sigreturn
> +		 * which are linked from the address 0 in vmlinux since
> +		 * vdso symbol addresses are actually used as an offset from
> +		 * mm->context.vdso in VDSO_OFFSET macro.
> +		 */
> +		if (relocated_addr >= KERNEL_LINK_ADDR)
> +			relocated_addr += reloc_offset;
> +
> +		*(Elf64_Addr *)addr = relocated_addr;
> +	}
> +}
> +#endif /* CONFIG_RELOCATABLE */
> +
>   #ifdef CONFIG_XIP_KERNEL
>   static void __init create_kernel_page_table(pgd_t *pgdir,
>   					    __always_unused bool early)
> @@ -1039,6 +1080,17 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>   	BUG_ON((kernel_map.virt_addr + kernel_map.size) > ADDRESS_SPACE_END - SZ_4K);
>   #endif
>   
> +#ifdef CONFIG_RELOCATABLE
> +	/*
> +	 * Early page table uses only one PUD, which makes it possible
> +	 * to map PUD_SIZE aligned on PUD_SIZE: if the relocation offset
> +	 * makes the kernel cross over a PUD_SIZE boundary, raise a bug
> +	 * since a part of the kernel would not get mapped.
> +	 */
> +	BUG_ON(PUD_SIZE - (kernel_map.virt_addr & (PUD_SIZE - 1)) < kernel_map.size);
> +	relocate_kernel();
> +#endif
> +
>   	apply_early_boot_alternatives();
>   	pt_ops_set_early();
>   

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^ permalink raw reply related	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-02-22 12:29   ` Alexandre Ghiti
@ 2023-02-24 15:58     ` Björn Töpel
  2023-03-22 18:25       ` Nick Desaulniers
  2023-03-22 13:38     ` Alexandre Ghiti
  1 sibling, 1 reply; 19+ messages in thread
From: Björn Töpel @ 2023-02-24 15:58 UTC (permalink / raw)
  To: Alexandre Ghiti, Alexandre Ghiti, Michael Ellerman,
	Nicholas Piggin, Christophe Leroy, Paul Walmsley, Palmer Dabbelt,
	Albert Ou, linuxppc-dev, linux-kernel, linux-riscv, nathan,
	linux-kbuild, llvm, ndesaulniers

Alexandre Ghiti <alex@ghiti.fr> writes:

> +cc linux-kbuild, llvm, Nathan, Nick
>
> On 2/15/23 15:36, Alexandre Ghiti wrote:
>> From: Alexandre Ghiti <alex@ghiti.fr>
>>
>> This config allows to compile 64b kernel as PIE and to relocate it at
>> any virtual address at runtime: this paves the way to KASLR.
>> Runtime relocation is possible since relocation metadata are embedded into
>> the kernel.
>>
>> Note that relocating at runtime introduces an overhead even if the
>> kernel is loaded at the same address it was linked at and that the compiler
>> options are those used in arm64 which uses the same RELA relocation
>> format.
>>
>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
>> ---
>>   arch/riscv/Kconfig              | 14 +++++++++
>>   arch/riscv/Makefile             |  7 +++--
>>   arch/riscv/kernel/efi-header.S  |  6 ++--
>>   arch/riscv/kernel/vmlinux.lds.S | 10 ++++--
>>   arch/riscv/mm/Makefile          |  4 +++
>>   arch/riscv/mm/init.c            | 54 ++++++++++++++++++++++++++++++++-
>>   6 files changed, 87 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index e2b656043abf..e0ee7ce4b2e3 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -544,6 +544,20 @@ config COMPAT
>>   
>>   	  If you want to execute 32-bit userspace applications, say Y.
>>   
>> +config RELOCATABLE
>> +	bool "Build a relocatable kernel"
>> +	depends on MMU && 64BIT && !XIP_KERNEL
>> +	help
>> +          This builds a kernel as a Position Independent Executable (PIE),
>> +          which retains all relocation metadata required to relocate the
>> +          kernel binary at runtime to a different virtual address than the
>> +          address it was linked at.
>> +          Since RISCV uses the RELA relocation format, this requires a
>> +          relocation pass at runtime even if the kernel is loaded at the
>> +          same address it was linked at.
>> +
>> +          If unsure, say N.
>> +
>>   endmenu # "Kernel features"
>>   
>>   menu "Boot options"
>> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
>> index 82153960ac00..97c34136b027 100644
>> --- a/arch/riscv/Makefile
>> +++ b/arch/riscv/Makefile
>> @@ -7,9 +7,12 @@
>>   #
>>   
>>   OBJCOPYFLAGS    := -O binary
>> -LDFLAGS_vmlinux :=
>> +ifeq ($(CONFIG_RELOCATABLE),y)
>> +	LDFLAGS_vmlinux += -shared -Bsymbolic -z notext -z norelro
>> +	KBUILD_CFLAGS += -fPIE
>> +endif
>>   ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
>> -	LDFLAGS_vmlinux := --no-relax
>> +	LDFLAGS_vmlinux += --no-relax
>>   	KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
>>   	CC_FLAGS_FTRACE := -fpatchable-function-entry=8
>>   endif
>> diff --git a/arch/riscv/kernel/efi-header.S b/arch/riscv/kernel/efi-header.S
>> index 8e733aa48ba6..f7ee09c4f12d 100644
>> --- a/arch/riscv/kernel/efi-header.S
>> +++ b/arch/riscv/kernel/efi-header.S
>> @@ -33,7 +33,7 @@ optional_header:
>>   	.byte	0x02					// MajorLinkerVersion
>>   	.byte	0x14					// MinorLinkerVersion
>>   	.long	__pecoff_text_end - efi_header_end	// SizeOfCode
>> -	.long	__pecoff_data_virt_size			// SizeOfInitializedData
>> +	.long	__pecoff_data_virt_end - __pecoff_text_end	// SizeOfInitializedData
>>   	.long	0					// SizeOfUninitializedData
>>   	.long	__efistub_efi_pe_entry - _start		// AddressOfEntryPoint
>>   	.long	efi_header_end - _start			// BaseOfCode
>> @@ -91,9 +91,9 @@ section_table:
>>   		IMAGE_SCN_MEM_EXECUTE			// Characteristics
>>   
>>   	.ascii	".data\0\0\0"
>> -	.long	__pecoff_data_virt_size			// VirtualSize
>> +	.long	__pecoff_data_virt_end - __pecoff_text_end	// VirtualSize
>>   	.long	__pecoff_text_end - _start		// VirtualAddress
>> -	.long	__pecoff_data_raw_size			// SizeOfRawData
>> +	.long	__pecoff_data_raw_end - __pecoff_text_end	// SizeOfRawData
>>   	.long	__pecoff_text_end - _start		// PointerToRawData
>>   
>>   	.long	0					// PointerToRelocations
>> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
>> index 4e6c88aa4d87..8be2de3be08c 100644
>> --- a/arch/riscv/kernel/vmlinux.lds.S
>> +++ b/arch/riscv/kernel/vmlinux.lds.S
>> @@ -122,9 +122,15 @@ SECTIONS
>>   		*(.sdata*)
>>   	}
>>   
>> +	.rela.dyn : ALIGN(8) {
>> +		__rela_dyn_start = .;
>> +		*(.rela .rela*)
>> +		__rela_dyn_end = .;
>> +	}
>> +
>
>
> So I realized those relocations would be better in the init section so 
> we can get rid of them at some point. So I tried the following:
>
> diff --git a/arch/riscv/kernel/vmlinux.lds.S 
> b/arch/riscv/kernel/vmlinux.lds.S
> index 7ac215467fd5..6111023a89ef 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -93,6 +93,12 @@ SECTIONS
>                  *(.rel.dyn*)
>          }
>
> +       .rela.dyn : ALIGN(8) {
> +               __rela_dyn_start = .;
> +               *(.rela .rela*)
> +               __rela_dyn_end = .;
> +       }
> +
>          __init_data_end = .;
>
>          . = ALIGN(8);
> @@ -119,12 +125,6 @@ SECTIONS
>                  *(.sdata*)
>          }
>
> -       .rela.dyn : ALIGN(8) {
> -               __rela_dyn_start = .;
> -               *(.rela .rela*)
> -               __rela_dyn_end = .;
> -       }
> -
>   #ifdef CONFIG_EFI
>          .pecoff_edata_padding : { BYTE(0); . = 
> ALIGN(PECOFF_FILE_ALIGNMENT); }
>          __pecoff_data_raw_end = ABSOLUTE(.);
>
>
> But then all the relocations in vmlinux end up being null:
>
> vmlinux:     file format elf64-littleriscv
>
> $ riscv64-linux-gnu-objdump -R vmlinux
>
> DYNAMIC RELOCATION RECORDS
> OFFSET           TYPE              VALUE
> 0000000000000000 R_RISCV_NONE      *ABS*
> 0000000000000000 R_RISCV_NONE      *ABS*
> ....
>
>   I also noticed that re-linking vmlinux with the same command right 
> after works (ie, the relocations are now valid):
>
> $ riscv64-linux-gnu-objdump -R vmlinux
>
> vmlinux:     file format elf64-littleriscv
>
> DYNAMIC RELOCATION RECORDS
> OFFSET           TYPE              VALUE
> ffffffff82600718 R_RISCV_RELATIVE  *ABS*-0x000000007d9ff8e8
> ffffffff82600720 R_RISCV_RELATIVE  *ABS*-0x000000007d9ff8e8
> ...
>
> Below is the command used to generate this working vmlinux:
>
> riscv64-unknown-linux-gnu-ld -melf64lriscv -z noexecstack 
> --no-warn-rwx-segments -shared -Bsymbolic -z notext -z norelro 
> --no-relax --build-id=sha1 --script=./arch/riscv/kernel/vmlinux.lds 
> -Map=vmlinux.map -o vmlinux --whole-archive vmlinux.a .vmlinux.export.o 
> init/version-timestamp.o --no-whole-archive --start-group 
> ./drivers/firmware/efi/libstub/lib.a --end-group .tmp_vmlinux.kallsyms3.o
>
> I tried a lot of things, but I struggle to understand, does anyone have 
> any idea? FYI, the same problem happens with LLVM.

Don't ask me *why*, but adding --emit-relocs to your linker flags solves
"the NULL .rela.dyn" both for GCC and LLVM.

The downside is that you end up with a bunch of .rela cruft in your
vmlinux.


Björn

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^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-02-22 12:29   ` Alexandre Ghiti
  2023-02-24 15:58     ` Björn Töpel
@ 2023-03-22 13:38     ` Alexandre Ghiti
  1 sibling, 0 replies; 19+ messages in thread
From: Alexandre Ghiti @ 2023-03-22 13:38 UTC (permalink / raw)
  To: Alexandre Ghiti, Michael Ellerman, Nicholas Piggin,
	Christophe Leroy, Paul Walmsley, Palmer Dabbelt, Albert Ou,
	linuxppc-dev, linux-kernel, linux-riscv, nathan, linux-kbuild,
	llvm, ndesaulniers, Björn Töpel

@linux-kbuild: Does anyone has an idea to solve this?

Thanks!

On 2/22/23 13:29, Alexandre Ghiti wrote:
> +cc linux-kbuild, llvm, Nathan, Nick
>
> On 2/15/23 15:36, Alexandre Ghiti wrote:
>> From: Alexandre Ghiti <alex@ghiti.fr>
>>
>> This config allows to compile 64b kernel as PIE and to relocate it at
>> any virtual address at runtime: this paves the way to KASLR.
>> Runtime relocation is possible since relocation metadata are embedded 
>> into
>> the kernel.
>>
>> Note that relocating at runtime introduces an overhead even if the
>> kernel is loaded at the same address it was linked at and that the 
>> compiler
>> options are those used in arm64 which uses the same RELA relocation
>> format.
>>
>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
>> ---
>>   arch/riscv/Kconfig              | 14 +++++++++
>>   arch/riscv/Makefile             |  7 +++--
>>   arch/riscv/kernel/efi-header.S  |  6 ++--
>>   arch/riscv/kernel/vmlinux.lds.S | 10 ++++--
>>   arch/riscv/mm/Makefile          |  4 +++
>>   arch/riscv/mm/init.c            | 54 ++++++++++++++++++++++++++++++++-
>>   6 files changed, 87 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index e2b656043abf..e0ee7ce4b2e3 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -544,6 +544,20 @@ config COMPAT
>>           If you want to execute 32-bit userspace applications, say Y.
>>   +config RELOCATABLE
>> +    bool "Build a relocatable kernel"
>> +    depends on MMU && 64BIT && !XIP_KERNEL
>> +    help
>> +          This builds a kernel as a Position Independent Executable 
>> (PIE),
>> +          which retains all relocation metadata required to relocate 
>> the
>> +          kernel binary at runtime to a different virtual address 
>> than the
>> +          address it was linked at.
>> +          Since RISCV uses the RELA relocation format, this requires a
>> +          relocation pass at runtime even if the kernel is loaded at 
>> the
>> +          same address it was linked at.
>> +
>> +          If unsure, say N.
>> +
>>   endmenu # "Kernel features"
>>     menu "Boot options"
>> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
>> index 82153960ac00..97c34136b027 100644
>> --- a/arch/riscv/Makefile
>> +++ b/arch/riscv/Makefile
>> @@ -7,9 +7,12 @@
>>   #
>>     OBJCOPYFLAGS    := -O binary
>> -LDFLAGS_vmlinux :=
>> +ifeq ($(CONFIG_RELOCATABLE),y)
>> +    LDFLAGS_vmlinux += -shared -Bsymbolic -z notext -z norelro
>> +    KBUILD_CFLAGS += -fPIE
>> +endif
>>   ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
>> -    LDFLAGS_vmlinux := --no-relax
>> +    LDFLAGS_vmlinux += --no-relax
>>       KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
>>       CC_FLAGS_FTRACE := -fpatchable-function-entry=8
>>   endif
>> diff --git a/arch/riscv/kernel/efi-header.S 
>> b/arch/riscv/kernel/efi-header.S
>> index 8e733aa48ba6..f7ee09c4f12d 100644
>> --- a/arch/riscv/kernel/efi-header.S
>> +++ b/arch/riscv/kernel/efi-header.S
>> @@ -33,7 +33,7 @@ optional_header:
>>       .byte    0x02                    // MajorLinkerVersion
>>       .byte    0x14                    // MinorLinkerVersion
>>       .long    __pecoff_text_end - efi_header_end    // SizeOfCode
>> -    .long    __pecoff_data_virt_size            // 
>> SizeOfInitializedData
>> +    .long    __pecoff_data_virt_end - __pecoff_text_end    // 
>> SizeOfInitializedData
>>       .long    0                    // SizeOfUninitializedData
>>       .long    __efistub_efi_pe_entry - _start        // 
>> AddressOfEntryPoint
>>       .long    efi_header_end - _start            // BaseOfCode
>> @@ -91,9 +91,9 @@ section_table:
>>           IMAGE_SCN_MEM_EXECUTE            // Characteristics
>>         .ascii    ".data\0\0\0"
>> -    .long    __pecoff_data_virt_size            // VirtualSize
>> +    .long    __pecoff_data_virt_end - __pecoff_text_end    // 
>> VirtualSize
>>       .long    __pecoff_text_end - _start        // VirtualAddress
>> -    .long    __pecoff_data_raw_size            // SizeOfRawData
>> +    .long    __pecoff_data_raw_end - __pecoff_text_end    // 
>> SizeOfRawData
>>       .long    __pecoff_text_end - _start        // PointerToRawData
>>         .long    0                    // PointerToRelocations
>> diff --git a/arch/riscv/kernel/vmlinux.lds.S 
>> b/arch/riscv/kernel/vmlinux.lds.S
>> index 4e6c88aa4d87..8be2de3be08c 100644
>> --- a/arch/riscv/kernel/vmlinux.lds.S
>> +++ b/arch/riscv/kernel/vmlinux.lds.S
>> @@ -122,9 +122,15 @@ SECTIONS
>>           *(.sdata*)
>>       }
>>   +    .rela.dyn : ALIGN(8) {
>> +        __rela_dyn_start = .;
>> +        *(.rela .rela*)
>> +        __rela_dyn_end = .;
>> +    }
>> +
>
>
> So I realized those relocations would be better in the init section so 
> we can get rid of them at some point. So I tried the following:
>
> diff --git a/arch/riscv/kernel/vmlinux.lds.S 
> b/arch/riscv/kernel/vmlinux.lds.S
> index 7ac215467fd5..6111023a89ef 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -93,6 +93,12 @@ SECTIONS
>                 *(.rel.dyn*)
>         }
>
> +       .rela.dyn : ALIGN(8) {
> +               __rela_dyn_start = .;
> +               *(.rela .rela*)
> +               __rela_dyn_end = .;
> +       }
> +
>         __init_data_end = .;
>
>         . = ALIGN(8);
> @@ -119,12 +125,6 @@ SECTIONS
>                 *(.sdata*)
>         }
>
> -       .rela.dyn : ALIGN(8) {
> -               __rela_dyn_start = .;
> -               *(.rela .rela*)
> -               __rela_dyn_end = .;
> -       }
> -
>  #ifdef CONFIG_EFI
>         .pecoff_edata_padding : { BYTE(0); . = 
> ALIGN(PECOFF_FILE_ALIGNMENT); }
>         __pecoff_data_raw_end = ABSOLUTE(.);
>
>
> But then all the relocations in vmlinux end up being null:
>
> vmlinux:     file format elf64-littleriscv
>
> $ riscv64-linux-gnu-objdump -R vmlinux
>
> DYNAMIC RELOCATION RECORDS
> OFFSET           TYPE              VALUE
> 0000000000000000 R_RISCV_NONE      *ABS*
> 0000000000000000 R_RISCV_NONE      *ABS*
> ....
>
>  I also noticed that re-linking vmlinux with the same command right 
> after works (ie, the relocations are now valid):
>
> $ riscv64-linux-gnu-objdump -R vmlinux
>
> vmlinux:     file format elf64-littleriscv
>
> DYNAMIC RELOCATION RECORDS
> OFFSET           TYPE              VALUE
> ffffffff82600718 R_RISCV_RELATIVE  *ABS*-0x000000007d9ff8e8
> ffffffff82600720 R_RISCV_RELATIVE  *ABS*-0x000000007d9ff8e8
> ...
>
> Below is the command used to generate this working vmlinux:
>
> riscv64-unknown-linux-gnu-ld -melf64lriscv -z noexecstack 
> --no-warn-rwx-segments -shared -Bsymbolic -z notext -z norelro 
> --no-relax --build-id=sha1 --script=./arch/riscv/kernel/vmlinux.lds 
> -Map=vmlinux.map -o vmlinux --whole-archive vmlinux.a 
> .vmlinux.export.o init/version-timestamp.o --no-whole-archive 
> --start-group ./drivers/firmware/efi/libstub/lib.a --end-group 
> .tmp_vmlinux.kallsyms3.o
>
> I tried a lot of things, but I struggle to understand, does anyone 
> have any idea? FYI, the same problem happens with LLVM.
>
> Thanks,
>
> Alex
>
>
>>   #ifdef CONFIG_EFI
>>       .pecoff_edata_padding : { BYTE(0); . = 
>> ALIGN(PECOFF_FILE_ALIGNMENT); }
>> -    __pecoff_data_raw_size = ABSOLUTE(. - __pecoff_text_end);
>> +    __pecoff_data_raw_end = ABSOLUTE(.);
>>   #endif
>>         /* End of data section */
>> @@ -134,7 +140,7 @@ SECTIONS
>>     #ifdef CONFIG_EFI
>>       . = ALIGN(PECOFF_SECTION_ALIGNMENT);
>> -    __pecoff_data_virt_size = ABSOLUTE(. - __pecoff_text_end);
>> +    __pecoff_data_virt_end = ABSOLUTE(.);
>>   #endif
>>       _end = .;
>>   diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
>> index 2ac177c05352..b85e9e82f082 100644
>> --- a/arch/riscv/mm/Makefile
>> +++ b/arch/riscv/mm/Makefile
>> @@ -1,6 +1,10 @@
>>   # SPDX-License-Identifier: GPL-2.0-only
>>     CFLAGS_init.o := -mcmodel=medany
>> +ifdef CONFIG_RELOCATABLE
>> +CFLAGS_init.o += -fno-pie
>> +endif
>> +
>>   ifdef CONFIG_FTRACE
>>   CFLAGS_REMOVE_init.o = $(CC_FLAGS_FTRACE)
>>   CFLAGS_REMOVE_cacheflush.o = $(CC_FLAGS_FTRACE)
>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>> index 7f01c2e56efe..3862696c2ac9 100644
>> --- a/arch/riscv/mm/init.c
>> +++ b/arch/riscv/mm/init.c
>> @@ -20,6 +20,9 @@
>>   #include <linux/dma-map-ops.h>
>>   #include <linux/crash_dump.h>
>>   #include <linux/hugetlb.h>
>> +#ifdef CONFIG_RELOCATABLE
>> +#include <linux/elf.h>
>> +#endif
>>     #include <asm/fixmap.h>
>>   #include <asm/tlbflush.h>
>> @@ -146,7 +149,7 @@ static void __init print_vm_layout(void)
>>           print_ml("kasan", KASAN_SHADOW_START, KASAN_SHADOW_END);
>>   #endif
>>   -        print_ml("kernel", (unsigned long)KERNEL_LINK_ADDR,
>> +        print_ml("kernel", (unsigned long)kernel_map.virt_addr,
>>                (unsigned long)ADDRESS_SPACE_END);
>>       }
>>   }
>> @@ -854,6 +857,44 @@ static __init void set_satp_mode(uintptr_t dtb_pa)
>>   #error "setup_vm() is called from head.S before relocate so it 
>> should not use absolute addressing."
>>   #endif
>>   +#ifdef CONFIG_RELOCATABLE
>> +extern unsigned long __rela_dyn_start, __rela_dyn_end;
>> +
>> +static void __init relocate_kernel(void)
>> +{
>> +    Elf64_Rela *rela = (Elf64_Rela *)&__rela_dyn_start;
>> +    /*
>> +     * This holds the offset between the linked virtual address and the
>> +     * relocated virtual address.
>> +     */
>> +    uintptr_t reloc_offset = kernel_map.virt_addr - KERNEL_LINK_ADDR;
>> +    /*
>> +     * This holds the offset between kernel linked virtual address and
>> +     * physical address.
>> +     */
>> +    uintptr_t va_kernel_link_pa_offset = KERNEL_LINK_ADDR - 
>> kernel_map.phys_addr;
>> +
>> +    for ( ; rela < (Elf64_Rela *)&__rela_dyn_end; rela++) {
>> +        Elf64_Addr addr = (rela->r_offset - va_kernel_link_pa_offset);
>> +        Elf64_Addr relocated_addr = rela->r_addend;
>> +
>> +        if (rela->r_info != R_RISCV_RELATIVE)
>> +            continue;
>> +
>> +        /*
>> +         * Make sure to not relocate vdso symbols like rt_sigreturn
>> +         * which are linked from the address 0 in vmlinux since
>> +         * vdso symbol addresses are actually used as an offset from
>> +         * mm->context.vdso in VDSO_OFFSET macro.
>> +         */
>> +        if (relocated_addr >= KERNEL_LINK_ADDR)
>> +            relocated_addr += reloc_offset;
>> +
>> +        *(Elf64_Addr *)addr = relocated_addr;
>> +    }
>> +}
>> +#endif /* CONFIG_RELOCATABLE */
>> +
>>   #ifdef CONFIG_XIP_KERNEL
>>   static void __init create_kernel_page_table(pgd_t *pgdir,
>>                           __always_unused bool early)
>> @@ -1039,6 +1080,17 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>       BUG_ON((kernel_map.virt_addr + kernel_map.size) > 
>> ADDRESS_SPACE_END - SZ_4K);
>>   #endif
>>   +#ifdef CONFIG_RELOCATABLE
>> +    /*
>> +     * Early page table uses only one PUD, which makes it possible
>> +     * to map PUD_SIZE aligned on PUD_SIZE: if the relocation offset
>> +     * makes the kernel cross over a PUD_SIZE boundary, raise a bug
>> +     * since a part of the kernel would not get mapped.
>> +     */
>> +    BUG_ON(PUD_SIZE - (kernel_map.virt_addr & (PUD_SIZE - 1)) < 
>> kernel_map.size);
>> +    relocate_kernel();
>> +#endif
>> +
>>       apply_early_boot_alternatives();
>>       pt_ops_set_early();
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

_______________________________________________
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^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-02-24 15:58     ` Björn Töpel
@ 2023-03-22 18:25       ` Nick Desaulniers
  2023-03-23 20:01         ` Fangrui Song
  2023-03-24 10:34         ` Alexandre Ghiti
  0 siblings, 2 replies; 19+ messages in thread
From: Nick Desaulniers @ 2023-03-22 18:25 UTC (permalink / raw)
  To: Björn Töpel
  Cc: Alexandre Ghiti, Alexandre Ghiti, Michael Ellerman,
	Nicholas Piggin, Christophe Leroy, Paul Walmsley, Palmer Dabbelt,
	Albert Ou, linuxppc-dev, linux-kernel, linux-riscv, nathan,
	linux-kbuild, llvm

On Fri, Feb 24, 2023 at 7:58 AM Björn Töpel <bjorn@kernel.org> wrote:
>
> Alexandre Ghiti <alex@ghiti.fr> writes:
>
> > +cc linux-kbuild, llvm, Nathan, Nick
> >
> > On 2/15/23 15:36, Alexandre Ghiti wrote:
> >> From: Alexandre Ghiti <alex@ghiti.fr>
> >>
> > I tried a lot of things, but I struggle to understand, does anyone have
> > any idea? FYI, the same problem happens with LLVM.

Off the top of my head, no idea.

(Maybe as a follow up to this series, I wonder if pursuing
ARCH_HAS_RELR for ARCH=riscv is worthwhile?)

>
> Don't ask me *why*, but adding --emit-relocs to your linker flags solves
> "the NULL .rela.dyn" both for GCC and LLVM.
>
> The downside is that you end up with a bunch of .rela cruft in your
> vmlinux.

There was a patch just this week to use $(OBJCOPY) to strip these from
vmlinux (for x86). Looks like x86 uses --emit-relocs for KASLR:
https://lore.kernel.org/lkml/20230320121006.4863-1-petr.pavlu@suse.com/
-- 
Thanks,
~Nick Desaulniers

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-03-22 18:25       ` Nick Desaulniers
@ 2023-03-23 20:01         ` Fangrui Song
  2023-03-24 10:34         ` Alexandre Ghiti
  1 sibling, 0 replies; 19+ messages in thread
From: Fangrui Song @ 2023-03-23 20:01 UTC (permalink / raw)
  To: Nick Desaulniers
  Cc: Björn Töpel, Alexandre Ghiti, Alexandre Ghiti,
	Michael Ellerman, Nicholas Piggin, Christophe Leroy,
	Paul Walmsley, Palmer Dabbelt, Albert Ou, linuxppc-dev,
	linux-kernel, linux-riscv, nathan, linux-kbuild, llvm

On Wed, Mar 22, 2023 at 11:26 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Fri, Feb 24, 2023 at 7:58 AM Björn Töpel <bjorn@kernel.org> wrote:
> >
> > Alexandre Ghiti <alex@ghiti.fr> writes:
> >
> > > +cc linux-kbuild, llvm, Nathan, Nick
> > >
> > > On 2/15/23 15:36, Alexandre Ghiti wrote:
> > >> From: Alexandre Ghiti <alex@ghiti.fr>
> > >>
> > > I tried a lot of things, but I struggle to understand, does anyone have
> > > any idea? FYI, the same problem happens with LLVM.
>
> Off the top of my head, no idea.
>
> (Maybe as a follow up to this series, I wonder if pursuing
> ARCH_HAS_RELR for ARCH=riscv is worthwhile?)

(I had thought about this for my own fun, but the currently only
implementation arch/arm64/kernel/head.S uses assembly.
Every port needs to write some assembly for the same task, which is a pity.
In FreeBSD rtld, glibc, and musl, DT_RELR code is target-independent.)


> >
> > Don't ask me *why*, but adding --emit-relocs to your linker flags solves
> > "the NULL .rela.dyn" both for GCC and LLVM.
> >
> > The downside is that you end up with a bunch of .rela cruft in your
> > vmlinux.
>
> There was a patch just this week to use $(OBJCOPY) to strip these from
> vmlinux (for x86). Looks like x86 uses --emit-relocs for KASLR:
> https://lore.kernel.org/lkml/20230320121006.4863-1-petr.pavlu@suse.com/
> --
> Thanks,
> ~Nick Desaulniers
>


-- 
宋方睿

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^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-03-22 18:25       ` Nick Desaulniers
  2023-03-23 20:01         ` Fangrui Song
@ 2023-03-24 10:34         ` Alexandre Ghiti
  1 sibling, 0 replies; 19+ messages in thread
From: Alexandre Ghiti @ 2023-03-24 10:34 UTC (permalink / raw)
  To: Nick Desaulniers, Björn Töpel
  Cc: Alexandre Ghiti, Michael Ellerman, Nicholas Piggin,
	Christophe Leroy, Paul Walmsley, Palmer Dabbelt, Albert Ou,
	linuxppc-dev, linux-kernel, linux-riscv, nathan, linux-kbuild,
	llvm

Hi Nick,

On 3/22/23 19:25, Nick Desaulniers wrote:
> On Fri, Feb 24, 2023 at 7:58 AM Björn Töpel <bjorn@kernel.org> wrote:
>> Alexandre Ghiti <alex@ghiti.fr> writes:
>>
>>> +cc linux-kbuild, llvm, Nathan, Nick
>>>
>>> On 2/15/23 15:36, Alexandre Ghiti wrote:
>>>> From: Alexandre Ghiti <alex@ghiti.fr>
>>>>
>>> I tried a lot of things, but I struggle to understand, does anyone have
>>> any idea? FYI, the same problem happens with LLVM.
> Off the top of my head, no idea.
>
> (Maybe as a follow up to this series, I wonder if pursuing
> ARCH_HAS_RELR for ARCH=riscv is worthwhile?)


IIUC, the goal for using RELR is to reduce the size of a kernel image: 
right now, this is not my priority, but I'll add that to my todo list 
because that may be useful to distros.


>
>> Don't ask me *why*, but adding --emit-relocs to your linker flags solves
>> "the NULL .rela.dyn" both for GCC and LLVM.
>>
>> The downside is that you end up with a bunch of .rela cruft in your
>> vmlinux.
> There was a patch just this week to use $(OBJCOPY) to strip these from
> vmlinux (for x86). Looks like x86 uses --emit-relocs for KASLR:
> https://lore.kernel.org/lkml/20230320121006.4863-1-petr.pavlu@suse.com/


That's nice, that would be an interesting intermediate step until we 
find the issue here as I believe it is important to have the relocations 
in the init section to save memory.

Thanks for your answer Nick, really appreciated,

Alex



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^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-02-15 14:36 ` [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE Alexandre Ghiti
  2023-02-22 12:29   ` Alexandre Ghiti
@ 2023-05-09 19:07   ` Andreas Schwab
  2023-05-09 19:55     ` Alexandre Ghiti
  1 sibling, 1 reply; 19+ messages in thread
From: Andreas Schwab @ 2023-05-09 19:07 UTC (permalink / raw)
  To: Alexandre Ghiti
  Cc: Michael Ellerman, Nicholas Piggin, Christophe Leroy,
	Paul Walmsley, Palmer Dabbelt, Albert Ou, linuxppc-dev,
	linux-kernel, linux-riscv, Alexandre Ghiti

That does not work with UEFI booting:

Loading Linux 6.4.0-rc1-1.g668187d-default ...
Loading initial ramdisk ...
Unhandled exception: Instruction access fault
EPC: ffffffff80016d56 RA: 000000008020334e TVAL: 0000007f80016d56
EPC: ffffffff002d1d56 RA: 00000000004be34e reloc adjusted
Unhandled exception: Load access fault
EPC: 00000000fff462d4 RA: 00000000fff462d0 TVAL: ffffffff80016d56
EPC: 00000000802012d4 RA: 00000000802012d0 reloc adjusted

Code: c825 8e0d 05b3 40b4 d0ef 0636 7493 ffe4 (d783 0004)
UEFI image [0x00000000fe65e000:0x00000000fe6e3fff] '/efi\boot\bootriscv64.efi'
UEFI image [0x00000000daa82000:0x00000000dcc2afff]

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

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^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-05-09 19:07   ` Andreas Schwab
@ 2023-05-09 19:55     ` Alexandre Ghiti
  2023-05-11 18:18       ` Andreas Schwab
  0 siblings, 1 reply; 19+ messages in thread
From: Alexandre Ghiti @ 2023-05-09 19:55 UTC (permalink / raw)
  To: Andreas Schwab, Alexandre Ghiti
  Cc: Michael Ellerman, Nicholas Piggin, Christophe Leroy,
	Paul Walmsley, Palmer Dabbelt, Albert Ou, linuxppc-dev,
	linux-kernel, linux-riscv

On 5/9/23 21:07, Andreas Schwab wrote:
> That does not work with UEFI booting:
>
> Loading Linux 6.4.0-rc1-1.g668187d-default ...
> Loading initial ramdisk ...
> Unhandled exception: Instruction access fault
> EPC: ffffffff80016d56 RA: 000000008020334e TVAL: 0000007f80016d56
> EPC: ffffffff002d1d56 RA: 00000000004be34e reloc adjusted
> Unhandled exception: Load access fault
> EPC: 00000000fff462d4 RA: 00000000fff462d0 TVAL: ffffffff80016d56
> EPC: 00000000802012d4 RA: 00000000802012d0 reloc adjusted
>
> Code: c825 8e0d 05b3 40b4 d0ef 0636 7493 ffe4 (d783 0004)
> UEFI image [0x00000000fe65e000:0x00000000fe6e3fff] '/efi\boot\bootriscv64.efi'
> UEFI image [0x00000000daa82000:0x00000000dcc2afff]
>

I need more details please, as I have a UEFI bootflow and it works great 
(KASLR is based on a relocatable kernel and works fine in UEFI too).

Thanks,

Alex


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^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-05-09 19:55     ` Alexandre Ghiti
@ 2023-05-11 18:18       ` Andreas Schwab
  2023-05-12 18:41         ` Palmer Dabbelt
  2023-05-19 11:08         ` Alexandre Ghiti
  0 siblings, 2 replies; 19+ messages in thread
From: Andreas Schwab @ 2023-05-11 18:18 UTC (permalink / raw)
  To: Alexandre Ghiti
  Cc: Alexandre Ghiti, Michael Ellerman, Nicholas Piggin,
	Christophe Leroy, Paul Walmsley, Palmer Dabbelt, Albert Ou,
	linuxppc-dev, linux-kernel, linux-riscv

On Mai 09 2023, Alexandre Ghiti wrote:

> On 5/9/23 21:07, Andreas Schwab wrote:
>> That does not work with UEFI booting:
>>
>> Loading Linux 6.4.0-rc1-1.g668187d-default ...
>> Loading initial ramdisk ...
>> Unhandled exception: Instruction access fault
>> EPC: ffffffff80016d56 RA: 000000008020334e TVAL: 0000007f80016d56
>> EPC: ffffffff002d1d56 RA: 00000000004be34e reloc adjusted
>> Unhandled exception: Load access fault
>> EPC: 00000000fff462d4 RA: 00000000fff462d0 TVAL: ffffffff80016d56
>> EPC: 00000000802012d4 RA: 00000000802012d0 reloc adjusted
>>
>> Code: c825 8e0d 05b3 40b4 d0ef 0636 7493 ffe4 (d783 0004)
>> UEFI image [0x00000000fe65e000:0x00000000fe6e3fff] '/efi\boot\bootriscv64.efi'
>> UEFI image [0x00000000daa82000:0x00000000dcc2afff]
>>
>
> I need more details please, as I have a UEFI bootflow and it works great
> (KASLR is based on a relocatable kernel and works fine in UEFI too).

It also crashes without UEFI.  Disabling CONFIG_RELOCATABLE fixes that.
This was tested on the HiFive Unmatched board.
The kernel image I tested is available from
<https://download.opensuse.org/repositories/Kernel:/HEAD/RISCV/>.  The
same kernel with CONFIG_RELOCATABLE disabled is available from
<https://download.opensuse.org/repositories/home:/Andreas_Schwab:/riscv:/kernel/standard/>.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

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^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-05-11 18:18       ` Andreas Schwab
@ 2023-05-12 18:41         ` Palmer Dabbelt
  2023-05-19 11:08         ` Alexandre Ghiti
  1 sibling, 0 replies; 19+ messages in thread
From: Palmer Dabbelt @ 2023-05-12 18:41 UTC (permalink / raw)
  To: schwab
  Cc: alex, alexghiti, mpe, npiggin, christophe.leroy, Paul Walmsley,
	aou, linuxppc-dev, linux-kernel, linux-riscv

On Thu, 11 May 2023 11:18:23 PDT (-0700), schwab@linux-m68k.org wrote:
> On Mai 09 2023, Alexandre Ghiti wrote:
>
>> On 5/9/23 21:07, Andreas Schwab wrote:
>>> That does not work with UEFI booting:
>>>
>>> Loading Linux 6.4.0-rc1-1.g668187d-default ...
>>> Loading initial ramdisk ...
>>> Unhandled exception: Instruction access fault
>>> EPC: ffffffff80016d56 RA: 000000008020334e TVAL: 0000007f80016d56
>>> EPC: ffffffff002d1d56 RA: 00000000004be34e reloc adjusted
>>> Unhandled exception: Load access fault
>>> EPC: 00000000fff462d4 RA: 00000000fff462d0 TVAL: ffffffff80016d56
>>> EPC: 00000000802012d4 RA: 00000000802012d0 reloc adjusted
>>>
>>> Code: c825 8e0d 05b3 40b4 d0ef 0636 7493 ffe4 (d783 0004)
>>> UEFI image [0x00000000fe65e000:0x00000000fe6e3fff] '/efi\boot\bootriscv64.efi'
>>> UEFI image [0x00000000daa82000:0x00000000dcc2afff]
>>>
>>
>> I need more details please, as I have a UEFI bootflow and it works great
>> (KASLR is based on a relocatable kernel and works fine in UEFI too).
>
> It also crashes without UEFI.  Disabling CONFIG_RELOCATABLE fixes that.
> This was tested on the HiFive Unmatched board.
> The kernel image I tested is available from
> <https://download.opensuse.org/repositories/Kernel:/HEAD/RISCV/>.  The
> same kernel with CONFIG_RELOCATABLE disabled is available from
> <https://download.opensuse.org/repositories/home:/Andreas_Schwab:/riscv:/kernel/standard/>.

Sorry I missed this earlier, there's been some other reports of boot 
failures on rc1 showing up but those were all a lot more vague.  Just 
setting CONFIG_RELOCATABLE=y doesn't manifest a boot failure on QEMU on 
my end and I don't have an UNmatched floating around.

Alex says he's going to look into it (and IIRC he has my Unmatched...).

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^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-05-11 18:18       ` Andreas Schwab
  2023-05-12 18:41         ` Palmer Dabbelt
@ 2023-05-19 11:08         ` Alexandre Ghiti
  2023-05-19 21:48           ` Andreas Schwab
  1 sibling, 1 reply; 19+ messages in thread
From: Alexandre Ghiti @ 2023-05-19 11:08 UTC (permalink / raw)
  To: Andreas Schwab
  Cc: Alexandre Ghiti, Michael Ellerman, Nicholas Piggin,
	Christophe Leroy, Paul Walmsley, Palmer Dabbelt, Albert Ou,
	linuxppc-dev, linux-kernel, linux-riscv

On 5/11/23 20:18, Andreas Schwab wrote:
> On Mai 09 2023, Alexandre Ghiti wrote:
>
>> On 5/9/23 21:07, Andreas Schwab wrote:
>>> That does not work with UEFI booting:
>>>
>>> Loading Linux 6.4.0-rc1-1.g668187d-default ...
>>> Loading initial ramdisk ...
>>> Unhandled exception: Instruction access fault
>>> EPC: ffffffff80016d56 RA: 000000008020334e TVAL: 0000007f80016d56
>>> EPC: ffffffff002d1d56 RA: 00000000004be34e reloc adjusted
>>> Unhandled exception: Load access fault
>>> EPC: 00000000fff462d4 RA: 00000000fff462d0 TVAL: ffffffff80016d56
>>> EPC: 00000000802012d4 RA: 00000000802012d0 reloc adjusted
>>>
>>> Code: c825 8e0d 05b3 40b4 d0ef 0636 7493 ffe4 (d783 0004)
>>> UEFI image [0x00000000fe65e000:0x00000000fe6e3fff] '/efi\boot\bootriscv64.efi'
>>> UEFI image [0x00000000daa82000:0x00000000dcc2afff]
>>>
>> I need more details please, as I have a UEFI bootflow and it works great
>> (KASLR is based on a relocatable kernel and works fine in UEFI too).
> It also crashes without UEFI.  Disabling CONFIG_RELOCATABLE fixes that.
> This was tested on the HiFive Unmatched board.
> The kernel image I tested is available from
> <https://download.opensuse.org/repositories/Kernel:/HEAD/RISCV/>.  The
> same kernel with CONFIG_RELOCATABLE disabled is available from
> <https://download.opensuse.org/repositories/home:/Andreas_Schwab:/riscv:/kernel/standard/>.
>

I have tested the following patch successfully, can you give it a try 
while I make sure this is the only place I forgot to add the -fno-pie flag?

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index fbdccc21418a..153864e4f399 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -23,6 +23,10 @@ ifdef CONFIG_FTRACE
  CFLAGS_REMOVE_alternative.o = $(CC_FLAGS_FTRACE)
  CFLAGS_REMOVE_cpufeature.o = $(CC_FLAGS_FTRACE)
  endif
+ifdef CONFIG_RELOCATABLE
+CFLAGS_alternative.o += -fno-pie
+CFLAGS_cpufeature.o += -fno-pie
+endif
  ifdef CONFIG_KASAN
  KASAN_SANITIZE_alternative.o := n
  KASAN_SANITIZE_cpufeature.o := n

Thanks

Alex


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^ permalink raw reply related	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-05-19 11:08         ` Alexandre Ghiti
@ 2023-05-19 21:48           ` Andreas Schwab
  2023-05-19 21:55             ` Palmer Dabbelt
  0 siblings, 1 reply; 19+ messages in thread
From: Andreas Schwab @ 2023-05-19 21:48 UTC (permalink / raw)
  To: Alexandre Ghiti
  Cc: Alexandre Ghiti, Michael Ellerman, Nicholas Piggin,
	Christophe Leroy, Paul Walmsley, Palmer Dabbelt, Albert Ou,
	linuxppc-dev, linux-kernel, linux-riscv

On Mai 19 2023, Alexandre Ghiti wrote:

> I have tested the following patch successfully, can you give it a try
> while I make sure this is the only place I forgot to add the -fno-pie
> flag?
>
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index fbdccc21418a..153864e4f399 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -23,6 +23,10 @@ ifdef CONFIG_FTRACE
>  CFLAGS_REMOVE_alternative.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_cpufeature.o = $(CC_FLAGS_FTRACE)
>  endif
> +ifdef CONFIG_RELOCATABLE
> +CFLAGS_alternative.o += -fno-pie
> +CFLAGS_cpufeature.o += -fno-pie
> +endif
>  ifdef CONFIG_KASAN
>  KASAN_SANITIZE_alternative.o := n
>  KASAN_SANITIZE_cpufeature.o := n

I can confirm that this fixes the crash.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

_______________________________________________
linux-riscv mailing list
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http://lists.infradead.org/mailman/listinfo/linux-riscv

^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-05-19 21:48           ` Andreas Schwab
@ 2023-05-19 21:55             ` Palmer Dabbelt
  2023-05-22 10:48               ` Alexandre Ghiti
  0 siblings, 1 reply; 19+ messages in thread
From: Palmer Dabbelt @ 2023-05-19 21:55 UTC (permalink / raw)
  To: schwab
  Cc: alex, alexghiti, mpe, npiggin, christophe.leroy, Paul Walmsley,
	aou, linuxppc-dev, linux-kernel, linux-riscv

On Fri, 19 May 2023 14:48:59 PDT (-0700), schwab@linux-m68k.org wrote:
> On Mai 19 2023, Alexandre Ghiti wrote:
>
>> I have tested the following patch successfully, can you give it a try
>> while I make sure this is the only place I forgot to add the -fno-pie
>> flag?
>>
>> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
>> index fbdccc21418a..153864e4f399 100644
>> --- a/arch/riscv/kernel/Makefile
>> +++ b/arch/riscv/kernel/Makefile
>> @@ -23,6 +23,10 @@ ifdef CONFIG_FTRACE
>>  CFLAGS_REMOVE_alternative.o = $(CC_FLAGS_FTRACE)
>>  CFLAGS_REMOVE_cpufeature.o = $(CC_FLAGS_FTRACE)
>>  endif
>> +ifdef CONFIG_RELOCATABLE
>> +CFLAGS_alternative.o += -fno-pie
>> +CFLAGS_cpufeature.o += -fno-pie
>> +endif
>>  ifdef CONFIG_KASAN
>>  KASAN_SANITIZE_alternative.o := n
>>  KASAN_SANITIZE_cpufeature.o := n
>
> I can confirm that this fixes the crash.

Thanks.  Alex: can you send a patch?

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^ permalink raw reply	[flat|nested] 19+ messages in thread

* Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE
  2023-05-19 21:55             ` Palmer Dabbelt
@ 2023-05-22 10:48               ` Alexandre Ghiti
  0 siblings, 0 replies; 19+ messages in thread
From: Alexandre Ghiti @ 2023-05-22 10:48 UTC (permalink / raw)
  To: Palmer Dabbelt, schwab
  Cc: alexghiti, mpe, npiggin, christophe.leroy, Paul Walmsley, aou,
	linuxppc-dev, linux-kernel, linux-riscv


On 19/05/2023 23:55, Palmer Dabbelt wrote:
> On Fri, 19 May 2023 14:48:59 PDT (-0700), schwab@linux-m68k.org wrote:
>> On Mai 19 2023, Alexandre Ghiti wrote:
>>
>>> I have tested the following patch successfully, can you give it a try
>>> while I make sure this is the only place I forgot to add the -fno-pie
>>> flag?
>>>
>>> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
>>> index fbdccc21418a..153864e4f399 100644
>>> --- a/arch/riscv/kernel/Makefile
>>> +++ b/arch/riscv/kernel/Makefile
>>> @@ -23,6 +23,10 @@ ifdef CONFIG_FTRACE
>>>  CFLAGS_REMOVE_alternative.o = $(CC_FLAGS_FTRACE)
>>>  CFLAGS_REMOVE_cpufeature.o = $(CC_FLAGS_FTRACE)
>>>  endif
>>> +ifdef CONFIG_RELOCATABLE
>>> +CFLAGS_alternative.o += -fno-pie
>>> +CFLAGS_cpufeature.o += -fno-pie
>>> +endif
>>>  ifdef CONFIG_KASAN
>>>  KASAN_SANITIZE_alternative.o := n
>>>  KASAN_SANITIZE_cpufeature.o := n
>>
>> I can confirm that this fixes the crash.
>
> Thanks.  Alex: can you send a patch?


I don't think this patch alone will work, all the code in early 
alternatives must be compiled with -fno-pie, but I'm a bit scared that's 
a "big" constraint. For now, I see 2 solutions:

- Document somewhere the fact that anything called from early 
alternatives must be compiled with -fno-pie
- Or relocate once with physical address, call early alternatives, and 
then do the final virtual relocation

Both options can be cumbersome in their own way, if anyone has an 
opinion, I'd be happy to discuss that :)



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^ permalink raw reply	[flat|nested] 19+ messages in thread

end of thread, other threads:[~2023-05-22 10:48 UTC | newest]

Thread overview: 19+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-02-15 14:36 [PATCH v8 0/3] Introduce 64b relocatable kernel Alexandre Ghiti
2023-02-15 14:36 ` [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE Alexandre Ghiti
2023-02-22 12:29   ` Alexandre Ghiti
2023-02-24 15:58     ` Björn Töpel
2023-03-22 18:25       ` Nick Desaulniers
2023-03-23 20:01         ` Fangrui Song
2023-03-24 10:34         ` Alexandre Ghiti
2023-03-22 13:38     ` Alexandre Ghiti
2023-05-09 19:07   ` Andreas Schwab
2023-05-09 19:55     ` Alexandre Ghiti
2023-05-11 18:18       ` Andreas Schwab
2023-05-12 18:41         ` Palmer Dabbelt
2023-05-19 11:08         ` Alexandre Ghiti
2023-05-19 21:48           ` Andreas Schwab
2023-05-19 21:55             ` Palmer Dabbelt
2023-05-22 10:48               ` Alexandre Ghiti
2023-02-15 14:36 ` [PATCH v8 2/3] powerpc: Move script to check relocations at compile time in scripts/ Alexandre Ghiti
2023-02-15 14:36 ` [PATCH v8 3/3] riscv: Check relocations at compile time Alexandre Ghiti
2023-02-20  9:14 ` [PATCH v8 0/3] Introduce 64b relocatable kernel Björn Töpel

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