This series hunts the problems discovered after manual enabling of ARCH_WANT_LD_ORPHAN_WARN, notably the missing PAGE_ALIGNED_DATA() section affecting VDSO placement (marked for stable).
Compile and runtime tested on MIPS32R2 CPS board with no issues.
Since v1 [0]: - catch .got entries too as LLD may produce it (Nathan); - check for unwanted sections to be zero-sized instead of discarding (Fangrui).
[0] https://lore.kernel.org/linux-mips/20210104121729.46981-1-alobakin@pm.me
Alexander Lobakin (4): MIPS: vmlinux.lds.S: add missing PAGE_ALIGNED_DATA() section MIPS: vmlinux.lds.S: add ".gnu.attributes" to DISCARDS MIPS: vmlinux.lds.S: catch bad .got, .plt and .rel.dyn at link time MIPS: select ARCH_WANT_LD_ORPHAN_WARN
arch/mips/Kconfig | 1 + arch/mips/kernel/vmlinux.lds.S | 39 +++++++++++++++++++++++++++++++++- 2 files changed, 39 insertions(+), 1 deletion(-)
MIPS uses its own declaration of rwdata, and thus it should be kept in sync with the asm-generic one. Currently PAGE_ALIGNED_DATA() is missing from the linker script, which emits the following ld warnings:
mips-alpine-linux-musl-ld: warning: orphan section `.data..page_aligned' from `arch/mips/kernel/vdso.o' being placed in section `.data..page_aligned' mips-alpine-linux-musl-ld: warning: orphan section `.data..page_aligned' from `arch/mips/vdso/vdso-image.o' being placed in section `.data..page_aligned'
Add the necessary declaration, so the mentioned structures will be placed in vmlinux as intended:
ffffffff80630580 D __end_once ffffffff80630580 D __start___dyndbg ffffffff80630580 D __start_once ffffffff80630580 D __stop___dyndbg ffffffff80634000 d mips_vdso_data ffffffff80638000 d vdso_data ffffffff80638580 D _gp ffffffff8063c000 T __init_begin ffffffff8063c000 D _edata ffffffff8063c000 T _sinittext
->
ffffffff805a4000 D __end_init_task ffffffff805a4000 D __nosave_begin ffffffff805a4000 D __nosave_end ffffffff805a4000 d mips_vdso_data ffffffff805a8000 d vdso_data ffffffff805ac000 D mmlist_lock ffffffff805ac080 D tasklist_lock
Fixes: ebb5e78cc634 ("MIPS: Initial implementation of a VDSO") Cc: stable@vger.kernel.org # 4.4+ Signed-off-by: Alexander Lobakin alobakin@pm.me --- arch/mips/kernel/vmlinux.lds.S | 1 + 1 file changed, 1 insertion(+)
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S index 5e97e9d02f98..83e27a181206 100644 --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -90,6 +90,7 @@ SECTIONS
INIT_TASK_DATA(THREAD_SIZE) NOSAVE_DATA + PAGE_ALIGNED_DATA(PAGE_SIZE) CACHELINE_ALIGNED_DATA(1 << CONFIG_MIPS_L1_CACHE_SHIFT) READ_MOSTLY_DATA(1 << CONFIG_MIPS_L1_CACHE_SHIFT) DATA_DATA
Discard GNU attributes at link time as kernel doesn't use it at all. Solves a dozen of the following ld warnings (one per every file):
mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `arch/mips/kernel/head.o' being placed in section `.gnu.attributes' mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `init/main.o' being placed in section `.gnu.attributes'
Misc: sort DISCARDS section entries alphabetically.
Signed-off-by: Alexander Lobakin alobakin@pm.me --- arch/mips/kernel/vmlinux.lds.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S index 83e27a181206..5d6563970ab2 100644 --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -221,9 +221,10 @@ SECTIONS /* ABI crap starts here */ *(.MIPS.abiflags) *(.MIPS.options) + *(.eh_frame) + *(.gnu.attributes) *(.options) *(.pdr) *(.reginfo) - *(.eh_frame) } }
On Wed, Jan 06, 2021 at 08:08:19PM +0000, Alexander Lobakin wrote:
Discard GNU attributes at link time as kernel doesn't use it at all. Solves a dozen of the following ld warnings (one per every file):
mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `arch/mips/kernel/head.o' being placed in section `.gnu.attributes' mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `init/main.o' being placed in section `.gnu.attributes'
Misc: sort DISCARDS section entries alphabetically.
Hmm, I wonder what is causing the appearance of .eh_frame? With help I tracked down all the causes of this on x86, arm, and arm64, so that's why it's not in the asm-generic DISCARDS section. I suspect this could be cleaned up for mips too?
Similarly for .gnu.attributes. What is generating that? (Or, more specifically, why is it both being generated AND discarded?)
-Kees
Signed-off-by: Alexander Lobakin alobakin@pm.me
arch/mips/kernel/vmlinux.lds.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S index 83e27a181206..5d6563970ab2 100644 --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -221,9 +221,10 @@ SECTIONS /* ABI crap starts here */ *(.MIPS.abiflags) *(.MIPS.options)
*(.eh_frame)*(.gnu.attributes)
*(.eh_frame)}
2.30.0
From: Kees Cook keescook@chromium.org Date: Wed, 6 Jan 2021 14:07:07 -0800
On Wed, Jan 06, 2021 at 08:08:19PM +0000, Alexander Lobakin wrote:
Discard GNU attributes at link time as kernel doesn't use it at all. Solves a dozen of the following ld warnings (one per every file):
mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `arch/mips/kernel/head.o' being placed in section `.gnu.attributes' mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `init/main.o' being placed in section `.gnu.attributes'
Misc: sort DISCARDS section entries alphabetically.
Hmm, I wonder what is causing the appearance of .eh_frame? With help I tracked down all the causes of this on x86, arm, and arm64, so that's why it's not in the asm-generic DISCARDS section. I suspect this could be cleaned up for mips too?
I could take a look and hunt it down. Could you please give some refs on what were the causes and solutions for the mentioned architectures?
Similarly for .gnu.attributes. What is generating that? (Or, more specifically, why is it both being generated AND discarded?)
On my setup, GNU Attributes consist of MIPS FP type (soft) and (if I'm correct) MIPS GNU Hash tables.
-Kees
By the way. I've built the kernel with LLVM stack (and found several subjects for more patches) and, besides '.got', also got a fistful of '.data..compoundliteral*' symbols (drivers/mtd/nand/spi/, net/ipv6/ etc). Where should they be placed (rodata, rwdata, ...) or they are anomalies of some kind and should be fixed somehow?
Signed-off-by: Alexander Lobakin alobakin@pm.me
arch/mips/kernel/vmlinux.lds.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S index 83e27a181206..5d6563970ab2 100644 --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -221,9 +221,10 @@ SECTIONS /* ABI crap starts here */ *(.MIPS.abiflags) *(.MIPS.options)
*(.eh_frame)*(.gnu.attributes)
*(.eh_frame)}
2.30.0
-- Kees Cook
Thanks, Al
On Wed, Jan 06, 2021 at 10:36:38PM +0000, Alexander Lobakin wrote:
From: Kees Cook keescook@chromium.org Date: Wed, 6 Jan 2021 14:07:07 -0800
On Wed, Jan 06, 2021 at 08:08:19PM +0000, Alexander Lobakin wrote:
Discard GNU attributes at link time as kernel doesn't use it at all. Solves a dozen of the following ld warnings (one per every file):
mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `arch/mips/kernel/head.o' being placed in section `.gnu.attributes' mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `init/main.o' being placed in section `.gnu.attributes'
Misc: sort DISCARDS section entries alphabetically.
Hmm, I wonder what is causing the appearance of .eh_frame? With help I tracked down all the causes of this on x86, arm, and arm64, so that's why it's not in the asm-generic DISCARDS section. I suspect this could be cleaned up for mips too?
I could take a look and hunt it down. Could you please give some refs on what were the causes and solutions for the mentioned architectures?
Sure! Here are the ones I could find again:
34b4a5c54c42 ("arm64/kernel: Remove needless Call Frame Information annotations") 6e0a66d10c5b ("arm64/build: Remove .eh_frame* sections due to unwind tables") d1c0272bc1c0 ("x86/boot/compressed: Remove, discard, or assert for unwanted sections")
Similarly for .gnu.attributes. What is generating that? (Or, more specifically, why is it both being generated AND discarded?)
On my setup, GNU Attributes consist of MIPS FP type (soft) and (if I'm correct) MIPS GNU Hash tables.
Ah, right, the soft-float markings sound correct to discard, IIUC.
By the way. I've built the kernel with LLVM stack (and found several subjects for more patches) and, besides '.got', also got a fistful of '.data..compoundliteral*' symbols (drivers/mtd/nand/spi/, net/ipv6/ etc). Where should they be placed (rodata, rwdata, ...) or they are anomalies of some kind and should be fixed somehow?
Ah yeah, I've seen this before: https://lore.kernel.org/lkml/202010051345.2Q0cvqdM-lkp@intel.com/ https://lore.kernel.org/lkml/CAKwvOd=s53vUELe311VSjxt2_eQd+RGNCf__n+cV+R=PQ_...
And it looks like LTO trips over it too: https://lore.kernel.org/lkml/20201211184633.3213045-3-samitolvanen@google.co...
So I think the correct solution is to follow Sami's patch and add it to vmlinux.lds.h:
-#define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..LPBX* +#define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..L* .data..compoundliteral* ... -#define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]* -#define BSS_MAIN .bss .bss.[0-9a-zA-Z_]* +#define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]* .rodata..L* +#define BSS_MAIN .bss .bss.[0-9a-zA-Z_]* .bss..compoundliteral*
Can you include a patch for this in your series?
Thanks!
From: Kees Cook keescook@chromium.org Date: Wed, 6 Jan 2021 15:26:18 -0800
On Wed, Jan 06, 2021 at 10:36:38PM +0000, Alexander Lobakin wrote:
From: Kees Cook keescook@chromium.org Date: Wed, 6 Jan 2021 14:07:07 -0800
On Wed, Jan 06, 2021 at 08:08:19PM +0000, Alexander Lobakin wrote:
Discard GNU attributes at link time as kernel doesn't use it at all. Solves a dozen of the following ld warnings (one per every file):
mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `arch/mips/kernel/head.o' being placed in section `.gnu.attributes' mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `init/main.o' being placed in section `.gnu.attributes'
Misc: sort DISCARDS section entries alphabetically.
Hmm, I wonder what is causing the appearance of .eh_frame? With help I tracked down all the causes of this on x86, arm, and arm64, so that's why it's not in the asm-generic DISCARDS section. I suspect this could be cleaned up for mips too?
I could take a look and hunt it down. Could you please give some refs on what were the causes and solutions for the mentioned architectures?
Sure! Here are the ones I could find again:
34b4a5c54c42 ("arm64/kernel: Remove needless Call Frame Information annotations") 6e0a66d10c5b ("arm64/build: Remove .eh_frame* sections due to unwind tables") d1c0272bc1c0 ("x86/boot/compressed: Remove, discard, or assert for unwanted sections")
Similarly for .gnu.attributes. What is generating that? (Or, more specifically, why is it both being generated AND discarded?)
On my setup, GNU Attributes consist of MIPS FP type (soft) and (if I'm correct) MIPS GNU Hash tables.
Ah, right, the soft-float markings sound correct to discard, IIUC.
By the way. I've built the kernel with LLVM stack (and found several subjects for more patches) and, besides '.got', also got a fistful of '.data..compoundliteral*' symbols (drivers/mtd/nand/spi/, net/ipv6/ etc). Where should they be placed (rodata, rwdata, ...) or they are anomalies of some kind and should be fixed somehow?
Ah yeah, I've seen this before: https://lore.kernel.org/lkml/202010051345.2Q0cvqdM-lkp@intel.com/ https://lore.kernel.org/lkml/CAKwvOd=s53vUELe311VSjxt2_eQd+RGNCf__n+cV+R=PQ_...
And it looks like LTO trips over it too: https://lore.kernel.org/lkml/20201211184633.3213045-3-samitolvanen@google.co...
So I think the correct solution is to follow Sami's patch and add it to vmlinux.lds.h:
-#define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..LPBX* +#define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..L* .data..compoundliteral* ... -#define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]* -#define BSS_MAIN .bss .bss.[0-9a-zA-Z_]* +#define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]* .rodata..L* +#define BSS_MAIN .bss .bss.[0-9a-zA-Z_]* .bss..compoundliteral*
Can you include a patch for this in your series?
Thanks!
Thanks for the help! Hope now I caught them all properly in v3.
-- Kees Cook
Al
On Wed, Jan 6, 2021 at 2:07 PM Kees Cook keescook@chromium.org wrote:
On Wed, Jan 06, 2021 at 08:08:19PM +0000, Alexander Lobakin wrote:
Discard GNU attributes at link time as kernel doesn't use it at all. Solves a dozen of the following ld warnings (one per every file):
mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `arch/mips/kernel/head.o' being placed in section `.gnu.attributes' mips-alpine-linux-musl-ld: warning: orphan section `.gnu.attributes' from `init/main.o' being placed in section `.gnu.attributes'
Misc: sort DISCARDS section entries alphabetically.
Hmm, I wonder what is causing the appearance of .eh_frame? With help I tracked down all the causes of this on x86, arm, and arm64, so that's why it's not in the asm-generic DISCARDS section. I suspect this could be cleaned up for mips too?
On x86, 003602ad5516e59940de42e44c8d8033387bb363 "x86/*/Makefile: Use -fno-asynchronous-unwind-tables to suppress .eh_frame sections" noticed that some Makefiles redefined KBUILD_CFLAGS and dropped -fno-asynchronous-unwind-tables. Maybe mips has similar issues.
Similarly for .gnu.attributes. What is generating that? (Or, more specifically, why is it both being generated AND discarded?)
-Kees
gcc/config/mips/mips.c https://github.com/gcc-mirror/gcc/blob/master/gcc/config/mips/mips.c#L9965 .gnu_attribute 4, 0 does not produce .gnu.attributes (SHT_GNU_ATTRIBUTES) but there are likely code paths that a non-zero value is used... So .gnu_attributes is likely needed to be excluded.
Signed-off-by: Alexander Lobakin alobakin@pm.me
arch/mips/kernel/vmlinux.lds.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S index 83e27a181206..5d6563970ab2 100644 --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -221,9 +221,10 @@ SECTIONS /* ABI crap starts here */ *(.MIPS.abiflags) *(.MIPS.options)
*(.eh_frame)*(.gnu.attributes) *(.options) *(.pdr) *(.reginfo)
*(.eh_frame) }}
2.30.0
-- Kees Cook
Catch any symbols placed in .got, .got.plt, .plt, .rel.dyn or .rela.dyn and check for these sections to be zero-sized at link time.
At least two of them were noticed in real builds:
mips-alpine-linux-musl-ld: warning: orphan section `.rel.dyn' from `init/main.o' being placed in section `.rel.dyn'
ld.lld: warning: <internal>:(.got) is being placed in '.got'
Adopted from x86/kernel/vmlinux.lds.S.
Reported-by: Nathan Chancellor natechancellor@gmail.com # .got Suggested-by: Fangrui Song maskray@google.com # .rel.dyn Signed-off-by: Alexander Lobakin alobakin@pm.me --- arch/mips/kernel/vmlinux.lds.S | 35 ++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+)
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S index 5d6563970ab2..05eda9d9a7d5 100644 --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -227,4 +227,39 @@ SECTIONS *(.pdr) *(.reginfo) } + + /* + * Sections that should stay zero sized, which is safer to + * explicitly check instead of blindly discarding. + */ + + .got : { + *(.got) + *(.igot.*) + } + ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!") + + .got.plt (INFO) : { + *(.got.plt) + } + ASSERT(SIZEOF(.got.plt) == 0, "Unexpected GOT/PLT entries detected!") + + .plt : { + *(.plt) + *(.plt.*) + *(.iplt) + } + ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!") + + .rel.dyn : { + *(.rel.*) + *(.rel_*) + } + ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!") + + .rela.dyn : { + *(.rela.*) + *(.rela_*) + } + ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!") }
On Wed, Jan 6, 2021 at 12:08 PM Alexander Lobakin alobakin@pm.me wrote:
Catch any symbols placed in .got, .got.plt, .plt, .rel.dyn or .rela.dyn and check for these sections to be zero-sized at link time.
At least two of them were noticed in real builds:
mips-alpine-linux-musl-ld: warning: orphan section `.rel.dyn' from `init/main.o' being placed in section `.rel.dyn'
ld.lld: warning: <internal>:(.got) is being placed in '.got'
Adopted from x86/kernel/vmlinux.lds.S.
Reported-by: Nathan Chancellor natechancellor@gmail.com # .got Suggested-by: Fangrui Song maskray@google.com # .rel.dyn Signed-off-by: Alexander Lobakin alobakin@pm.me
arch/mips/kernel/vmlinux.lds.S | 35 ++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+)
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S index 5d6563970ab2..05eda9d9a7d5 100644 --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -227,4 +227,39 @@ SECTIONS *(.pdr) *(.reginfo) }
/** Sections that should stay zero sized, which is safer to* explicitly check instead of blindly discarding.*/.got : {*(.got)*(.igot.*)}ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!").got.plt (INFO) : {*(.got.plt)}ASSERT(SIZEOF(.got.plt) == 0, "Unexpected GOT/PLT entries detected!")
(INFO) drops the SHF_ALLOC flag from the output section (It does not mean "informational"). INFO is not need here. The diff from 815d680771ae09080d2da83dac2647c08cdf99ce "x86/build: Enforce an empty .got.plt section" is not needed.
.plt : {*(.plt)*(.plt.*)*(.iplt)}ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!").rel.dyn : {*(.rel.*)*(.rel_*)}ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!").rela.dyn : {*(.rela.*)*(.rela_*)}ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")}
x86 has both .rel.dyn and .rela.dyn because i386 psABI uses REL while x86-64 psABI uses RELA, but mips does not need .rela.dyn
-- 2.30.0
On Wed, Jan 06, 2021 at 08:08:29PM +0000, Alexander Lobakin wrote:
Catch any symbols placed in .got, .got.plt, .plt, .rel.dyn or .rela.dyn and check for these sections to be zero-sized at link time.
At least two of them were noticed in real builds:
mips-alpine-linux-musl-ld: warning: orphan section `.rel.dyn' from `init/main.o' being placed in section `.rel.dyn'
ld.lld: warning: <internal>:(.got) is being placed in '.got'
Adopted from x86/kernel/vmlinux.lds.S.
Reported-by: Nathan Chancellor natechancellor@gmail.com # .got Suggested-by: Fangrui Song maskray@google.com # .rel.dyn Signed-off-by: Alexander Lobakin alobakin@pm.me
arch/mips/kernel/vmlinux.lds.S | 35 ++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+)
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S index 5d6563970ab2..05eda9d9a7d5 100644 --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -227,4 +227,39 @@ SECTIONS *(.pdr) *(.reginfo) }
- /*
* Sections that should stay zero sized, which is safer to* explicitly check instead of blindly discarding.*/- .got : {
*(.got)*(.igot.*)- }
- ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
This assertion does trigger now.
$ make -skj"$(nproc)" ARCH=mips CROSS_COMPILE=mipsel-linux-gnu- LLVM=1 \ O=out/mipsel distclean malta_kvm_guest_defconfig all ... ld.lld: error: Unexpected GOT entries detected! ld.lld: error: Unexpected GOT entries detected! ...
- .got.plt (INFO) : {
*(.got.plt)- }
- ASSERT(SIZEOF(.got.plt) == 0, "Unexpected GOT/PLT entries detected!")
- .plt : {
*(.plt)*(.plt.*)*(.iplt)- }
- ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
- .rel.dyn : {
*(.rel.*)*(.rel_*)- }
- ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!")
- .rela.dyn : {
*(.rela.*)*(.rela_*)- }
- ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
}
2.30.0
From: Nathan Chancellor natechancellor@gmail.com Date: Wed, 6 Jan 2021 13:23:24 -0700
On Wed, Jan 06, 2021 at 08:08:29PM +0000, Alexander Lobakin wrote:
Catch any symbols placed in .got, .got.plt, .plt, .rel.dyn or .rela.dyn and check for these sections to be zero-sized at link time.
At least two of them were noticed in real builds:
mips-alpine-linux-musl-ld: warning: orphan section `.rel.dyn' from `init/main.o' being placed in section `.rel.dyn'
ld.lld: warning: <internal>:(.got) is being placed in '.got'
Adopted from x86/kernel/vmlinux.lds.S.
Reported-by: Nathan Chancellor natechancellor@gmail.com # .got Suggested-by: Fangrui Song maskray@google.com # .rel.dyn Signed-off-by: Alexander Lobakin alobakin@pm.me
arch/mips/kernel/vmlinux.lds.S | 35 ++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+)
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S index 5d6563970ab2..05eda9d9a7d5 100644 --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -227,4 +227,39 @@ SECTIONS *(.pdr) *(.reginfo) }
- /*
* Sections that should stay zero sized, which is safer to* explicitly check instead of blindly discarding.*/- .got : {
*(.got)*(.igot.*)- }
- ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
This assertion does trigger now.
$ make -skj"$(nproc)" ARCH=mips CROSS_COMPILE=mipsel-linux-gnu- LLVM=1 \ O=out/mipsel distclean malta_kvm_guest_defconfig all ... ld.lld: error: Unexpected GOT entries detected! ld.lld: error: Unexpected GOT entries detected! ...
Oops. I'll build my kernel with LLVM stack and dig into it deeper tomorrow.
- .got.plt (INFO) : {
*(.got.plt)- }
- ASSERT(SIZEOF(.got.plt) == 0, "Unexpected GOT/PLT entries detected!")
- .plt : {
*(.plt)*(.plt.*)*(.iplt)- }
- ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
- .rel.dyn : {
*(.rel.*)*(.rel_*)- }
- ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!")
- .rela.dyn : {
*(.rela.*)*(.rela_*)- }
- ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
}
2.30.0
Thanks, Al
Now, after that all the sections are explicitly described and declared in vmlinux.lds.S, we can enable ld orphan warnings to prevent from missing any new sections in future.
Signed-off-by: Alexander Lobakin alobakin@pm.me --- arch/mips/Kconfig | 1 + 1 file changed, 1 insertion(+)
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index d68df1febd25..d3e64cc0932b 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -18,6 +18,7 @@ config MIPS select ARCH_USE_QUEUED_SPINLOCKS select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU select ARCH_WANT_IPC_PARSE_VERSION + select ARCH_WANT_LD_ORPHAN_WARN select BUILDTIME_TABLE_SORT select CLONE_BACKWARDS select CPU_NO_EFFICIENT_FFS if (TARGET_ISA_REV < 1)
On Wed, Jan 06, 2021 at 08:08:46PM +0000, Alexander Lobakin wrote:
Now, after that all the sections are explicitly described and declared in vmlinux.lds.S, we can enable ld orphan warnings to prevent from missing any new sections in future.
Signed-off-by: Alexander Lobakin alobakin@pm.me
Reviewed-by: Kees Cook keescook@chromium.org
On Wed, Jan 06, 2021 at 08:08:14PM +0000, Alexander Lobakin wrote:
MIPS uses its own declaration of rwdata, and thus it should be kept in sync with the asm-generic one. Currently PAGE_ALIGNED_DATA() is missing from the linker script, which emits the following ld warnings:
mips-alpine-linux-musl-ld: warning: orphan section `.data..page_aligned' from `arch/mips/kernel/vdso.o' being placed in section `.data..page_aligned' mips-alpine-linux-musl-ld: warning: orphan section `.data..page_aligned' from `arch/mips/vdso/vdso-image.o' being placed in section `.data..page_aligned'
Add the necessary declaration, so the mentioned structures will be placed in vmlinux as intended:
ffffffff80630580 D __end_once ffffffff80630580 D __start___dyndbg ffffffff80630580 D __start_once ffffffff80630580 D __stop___dyndbg ffffffff80634000 d mips_vdso_data ffffffff80638000 d vdso_data ffffffff80638580 D _gp ffffffff8063c000 T __init_begin ffffffff8063c000 D _edata ffffffff8063c000 T _sinittext
->
ffffffff805a4000 D __end_init_task ffffffff805a4000 D __nosave_begin ffffffff805a4000 D __nosave_end ffffffff805a4000 d mips_vdso_data ffffffff805a8000 d vdso_data ffffffff805ac000 D mmlist_lock ffffffff805ac080 D tasklist_lock
Fixes: ebb5e78cc634 ("MIPS: Initial implementation of a VDSO") Cc: stable@vger.kernel.org # 4.4+ Signed-off-by: Alexander Lobakin alobakin@pm.me
Reviewed-by: Kees Cook keescook@chromium.org
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Alexander Lobakin -
Fāng-ruì Sòng -
Kees Cook -
Nathan Chancellor