On Tue, May 26, 2020 at 4:55 PM Sedat Dilek <[email protected]> wrote: > > On Tue, May 26, 2020 at 4:48 PM Sedat Dilek <[email protected]> wrote: > > > > On Tue, May 26, 2020 at 2:44 PM Sedat Dilek <[email protected]> wrote: > > > > > > On Tue, May 26, 2020 at 2:33 PM Sedat Dilek <[email protected]> wrote: > > > > > > > > On Tue, May 26, 2020 at 2:30 PM Ard Biesheuvel <[email protected]> wrote: > > > > > > > > > > On Tue, 26 May 2020 at 14:29, Sedat Dilek <[email protected]> > > > > > wrote: > > > > > > > > > > > > On Tue, May 26, 2020 at 12:59 AM Arvind Sankar > > > > > > <[email protected]> wrote: > > > > > > > > > > > > > > The compressed kernel currently contains bogus runtime > > > > > > > relocations in > > > > > > > the startup code in head_{32,64}.S, which are generated by the > > > > > > > linker, > > > > > > > but must not actually be processed at runtime. > > > > > > > > > > > > > > This generates warnings when linking with the BFD linker, and > > > > > > > errors > > > > > > > with LLD, which defaults to erroring on runtime relocations in > > > > > > > read-only > > > > > > > sections. It also requires the -z noreloc-overflow hack for the > > > > > > > 64-bit > > > > > > > kernel, which prevents us from linking it as -pie on an older BFD > > > > > > > linker > > > > > > > (<= 2.26) or on LLD, because the locations that are to be > > > > > > > apparently > > > > > > > relocated are only 32-bits in size and so cannot normally have > > > > > > > R_X86_64_RELATIVE relocations. > > > > > > > > > > > > > > This series aims to get rid of these relocations. It is based on > > > > > > > efi/next, where the latest patches touch the head code to > > > > > > > eliminate the > > > > > > > global offset table. > > > > > > > > > > > > > > The first patch is an independent fix for LLD, to avoid an orphan > > > > > > > section in arch/x86/boot/setup.elf. > > > > > > > > > > > > > > The second patch gets rid of almost all the relocations. It uses > > > > > > > standard PIC addressing technique for 32-bit, i.e. loading a > > > > > > > register > > > > > > > with the address of _GLOBAL_OFFSET_TABLE_ and then using GOTOFF > > > > > > > references to access variables. For 64-bit, there is 32-bit code > > > > > > > that > > > > > > > cannot use RIP-relative addressing, and also cannot use the 32-bit > > > > > > > method, since GOTOFF references are 64-bit only. This is instead > > > > > > > handled > > > > > > > using a macro to replace a reference like gdt with > > > > > > > (gdt-startup_32) > > > > > > > instead. The assembler will generate a PC32 relocation entry, with > > > > > > > addend set to (.-startup_32), and these will be replaced with > > > > > > > constants > > > > > > > at link time. This works as long as all the code using such > > > > > > > references > > > > > > > lives in the same section as startup_32, i.e. in .head.text. > > > > > > > > > > > > > > The third patch addresses a remaining issue with the BFD linker, > > > > > > > which > > > > > > > insists on generating runtime relocations for absolute symbols. > > > > > > > We use > > > > > > > z_input_len and z_output_len, defined in the generated piggy.S > > > > > > > file, as > > > > > > > symbols whose absolute "addresses" are actually the size of the > > > > > > > compressed payload and the size of the decompressed kernel image > > > > > > > respectively. LLD does not generate relocations for these two > > > > > > > symbols, > > > > > > > but the BFD linker does, prior to the upcoming 2.35. To get > > > > > > > around this, > > > > > > > piggy.S is extended to also define two u32 variables (in .rodata) > > > > > > > with > > > > > > > the lengths, and the head code is modified to use those instead > > > > > > > of the > > > > > > > symbol addresses. > > > > > > > > > > > > > > An alternative way to handle z_input_len/z_output_len would be to > > > > > > > just > > > > > > > include piggy.S in head_{32,64}.S instead of as a separate object > > > > > > > file, > > > > > > > since the GNU assembler doesn't generate relocations for symbols > > > > > > > set to > > > > > > > constants. > > > > > > > > > > > > > > The last patch adds a check in the linker script to ensure that no > > > > > > > runtime relocations get reintroduced. Since the GOT has been > > > > > > > eliminated > > > > > > > as well, the compressed kernel has no runtime relocations > > > > > > > whatsoever any > > > > > > > more. > > > > > > > > > > > > > > Changes from v1: > > > > > > > - Add .text.* to setup.ld instead of just .text.startup > > > > > > > - Rename the la() macro introduced in the second patch for 64-bit > > > > > > > to > > > > > > > rva(), and rework the explanatory comment. > > > > > > > - In the last patch, check both .rel.dyn and .rela.dyn, instead > > > > > > > of just > > > > > > > one per arch. > > > > > > > > > > > > > > > > > > > Hi, > > > > > > > > > > > > I would like to test this patchset v2 on top of Linux v5.7-rc7 > > > > > > together with: > > > > > > > > > > > > [1] x86/boot: Discard .discard.unreachable for > > > > > > arch/x86/boot/compressed/vmlinux > > > > > > [2] x86/boot: Correct relocation destination on old linkers > > > > > > > > > > > > I tried to pull efi/next on top of Linux v5.7-rc7 and cleaned up the > > > > > > merge problems, but I am not sure I did it correctly. > > > > > > So, which patches are really relevant from efi/next? > > > > > > > > > > > > What's your suggestions? > > > > > > > > > > > > > > > > efi/next is here: > > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git/log/?h=next > > > > > > > > > > You'll need the top 3 patches. > > > > > > > > Thanks /o\. > > > > > > > > - Sedat - > > > > > > Are those diffs correct when using "x86/boot: Correct relocation > > > destination on old linkers"? > > > > > > $ cat ../head_32_S.diff > > > diff --cc arch/x86/boot/compressed/head_32.S > > > index 064e895bad92,03557f2174bf..000000000000 > > > --- a/arch/x86/boot/compressed/head_32.S > > > +++ b/arch/x86/boot/compressed/head_32.S > > > @@@ -49,13 -49,17 +49,14 @@@ > > > * Position Independent Executable (PIE) so that linker won't optimize > > > * R_386_GOT32X relocation to its fixed symbol address. Older > > > * linkers generate R_386_32 relocations against locally defined > > > symbols, > > > - * _bss, _ebss, in PIE. It isn't wrong, just suboptimal compared > > > - * _bss, _ebss, _got, _egot and _end, in PIE. It isn't wrong, just less > > > - * optimal than R_386_RELATIVE. But the x86 kernel fails to properly > > > handle > > > ++ * _bss, _ebss, _end in PIE. It isn't wrong, just suboptimal compared > > > + * to R_386_RELATIVE. But the x86 kernel fails to properly handle > > > * R_386_32 relocations when relocating the kernel. To generate > > > - * R_386_RELATIVE relocations, we mark _bss and _ebss as hidden: > > > - * R_386_RELATIVE relocations, we mark _bss, _ebss, _got, _egot and > > > _end as > > > - * hidden: > > > ++ * R_386_RELATIVE relocations, we mark _bss, _ebss and _end as hidden: > > > */ > > > .hidden _bss > > > .hidden _ebss > > > - .hidden _got > > > - .hidden _egot > > > + .hidden _end > > > > > > __HEAD > > > SYM_FUNC_START(startup_32) > > > > > > $ cat ../head_64_S.diff > > > diff --cc arch/x86/boot/compressed/head_64.S > > > index 4b7ad1dfbea6,76d1d64d51e3..000000000000 > > > --- a/arch/x86/boot/compressed/head_64.S > > > +++ b/arch/x86/boot/compressed/head_64.S > > > @@@ -40,34 -40,11 +40,35 @@@ > > > */ > > > .hidden _bss > > > .hidden _ebss > > > - .hidden _got > > > - .hidden _egot > > > + .hidden _end > > > > > > __HEAD > > > + > > > +/* > > > + * This macro gives the relative virtual address of X, i.e. the offset > > > of X > > > + * from startup_32. This is the same as the link-time virtual address > > > of X, > > > + * since startup_32 is at 0, but defining it this way tells the > > > + * assembler/linker that we do not want the actual run-time address of > > > X. This > > > + * prevents the linker from trying to create unwanted run-time > > > relocation > > > + * entries for the reference when the compressed kernel is linked as > > > PIE. > > > + * > > > + * A reference X(%reg) will result in the link-time VA of X being > > > stored with > > > + * the instruction, and a run-time R_X86_64_RELATIVE relocation entry > > > that > > > + * adds the 64-bit base address where the kernel is loaded. > > > + * > > > + * Replacing it with (X-startup_32)(%reg) results in the offset being > > > stored, > > > + * and no run-time relocation. > > > + * > > > + * The macro should be used as a displacement with a base register > > > containing > > > + * the run-time address of startup_32 [i.e. rva(X)(%reg)], or as an > > > immediate > > > + * [$ rva(X)]. > > > + * > > > + * This macro can only be used from within the .head.text section, > > > since the > > > + * expression requires startup_32 to be in the same section as the code > > > being > > > + * assembled. > > > + */ > > > +#define rva(X) ((X) - startup_32) > > > + > > > .code32 > > > SYM_FUNC_START(startup_32) > > > /* > > > > > > Thanks. > > > > > > > With LLVM/Clang/LLD I see: > > > > mycompiler -Wp,-MD,arch/x86/boot/compressed/.kernel_info.o.d > > -nostdinc -isystem > > /home/dileks/src/llvm-toolchain/install/lib/clang/10.0.1rc1/include > > -I./arch/x86/include -I./arch/x86/include/generated -I./include > > -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi > > -I./include/uapi -I./include/generated/uapi -include > > ./include/linux/kconfig.h -D__KERNEL__ -Qunused-arguments -m64 -O2 > > -fno-strict-aliasing -fPIE -DDISABLE_BRANCH_PROFILING -mcmodel=small > > -mno-mmx -mno-sse -ffreestanding -fno-stack-protector > > -Wno-address-of-packed-member -Wno-gnu -Wno-pointer-sign > > -fmacro-prefix-map=./= -fno-asynchronous-unwind-tables -include > > hidden.h -D__ASSEMBLY__ -c -o > > arch/x86/boot/compressed/kernel_info.o > > arch/x86/boot/compressed/kernel_info.S > > <built-in>:345:10: fatal error: 'hidden.h' file not found > > #include "hidden.h" > > ^~~~~~~~~~ > > 1 error generated. > > make[5]: *** [scripts/Makefile.build:349: > > arch/x86/boot/compressed/kernel_info.o] Error 1 > > make[4]: *** [arch/x86/boot/Makefile:114: > > arch/x86/boot/compressed/vmlinux] Error 2 > > make[4]: *** Waiting for unfinished jobs.... > > > > mycompiler is a wrapper-script to use ccache * clang-10 as compiler. > > > > patchset to previous build: > > > > $ git log --no-merges --oneline > > 5.7.0-rc7-1-amd64-clang..5.7.0-rc7-2-amd64-clang > > 8b74901cb9e5 > > (for-5.7/x86-boot-remove-runtime-relocations-from-compressed-kernel-v2-nivedita76) > > x86/boot: Check that there are no runtime relocations > > 83fb1bc3b076 x86/boot: Remove runtime relocations from head_{32,64}.S > > fede23dacbbd x86/boot: Remove run-time relocations from .head.text code > > 3e5ea481b8fb x86/boot: Add .text.* to setup.ld > > bec910ba3d67 x86/boot/compressed: Get rid of GOT fixup code > > be834cee6f39 x86/boot/compressed: Force hidden visibility for all > > symbol references > > 9b7c7d8d2d7b x86/boot/compressed: Move .got.plt entries out of the .got > > section > > ba6a49f806a0 (for-5.7/kbuild-compressed-debug-info) Makefile: support > > compressed debug info > > a1fb11944d11 (for-5.7/x86-boot-nivedita76) x86/boot: Correct > > relocation destination on old linkers > > c70e3890058f (for-5.7/x86-build-maskray) x86/boot: Discard > > .discard.unreachable for arch/x86/boot/compressed/vmlinux > > > > $ find ./ -name hidden.h > > ./drivers/firmware/efi/libstub/hidden.h > > ./arch/x86/boot/compressed/hidden.h > > > > Any thoughts? > > > > Maybe this should be: > > [ arch/x86/boot/compressed/Makefile ] > > -KBUILD_CFLAGS += -include hidden.h > +KBUILD_CFLAGS += -include ./hidden.h >
NOPE. This works: [ arch/x86/boot/compressed/Makefile ] -KBUILD_CFLAGS += -include hidden.h +KBUILD_CFLAGS += -include ./arch/x86/boot/compressed/hidden.h $ ll arch/x86/boot/bzImage arch/x86/boot/compressed/vmlinux -rw-r--r-- 1 dileks dileks 6,5M Mai 26 17:05 arch/x86/boot/bzImage -rwxr-xr-x 1 dileks dileks 6,5M Mai 26 17:05 arch/x86/boot/compressed/vmlinux - Sedat -
