On March 4, 2024 1:23:11 PM PST, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
6.1-stable review patch. If anyone has any objections, please let me know.
From: Alexander Lobakin alexandr.lobakin@intel.com
commit 7734a0f31e99c433df3063bbb7e8ee5a16a2cb82 upstream.
After commit ce697ccee1a8 ("kbuild: remove head-y syntax"), I started digging whether x86 is ready for removing this old cruft. Removing its objects from the list makes the kernel unbootable. This applies only to bzImage, vmlinux still works correctly. The reason is that with no strict object order determined by the linker arguments, not the linker script, startup_64 can be placed not right at the beginning of the kernel. Here's vmlinux.map's beginning before removing:
ffffffff81000000 vmlinux.o:(.head.text) ffffffff81000000 startup_64 ffffffff81000070 secondary_startup_64 ffffffff81000075 secondary_startup_64_no_verify ffffffff81000160 verify_cpu
and after:
ffffffff81000000 vmlinux.o:(.head.text) ffffffff81000000 pvh_start_xen ffffffff81000080 startup_64 ffffffff810000f0 secondary_startup_64 ffffffff810000f5 secondary_startup_64_no_verify
Not a problem itself, but the self-extractor code has the address of that function hardcoded the beginning, not looking onto the ELF header, which always contains the address of startup_{32,64}().
So, instead of doing an "act of blind faith", just take the address from the ELF header and extract a relative offset to the entry point. The decompressor function already returns a pointer to the beginning of the kernel to the Asm code, which then jumps to it, so add that offset to the return value. This doesn't change anything for now, but allows to resign from the "head object list" for x86 and makes sure valid Kbuild or any other improvements won't break anything here in general.
Signed-off-by: Alexander Lobakin alexandr.lobakin@intel.com Signed-off-by: Ingo Molnar mingo@kernel.org Tested-by: Jiri Slaby jirislaby@kernel.org Cc: "H. Peter Anvin" hpa@zytor.com Cc: Linus Torvalds torvalds@linux-foundation.org Link: https://lore.kernel.org/r/20230109170403.4117105-2-alexandr.lobakin@intel.co... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
arch/x86/boot/compressed/head_32.S | 2 +- arch/x86/boot/compressed/head_64.S | 2 +- arch/x86/boot/compressed/misc.c | 18 +++++++++++------- 3 files changed, 13 insertions(+), 9 deletions(-)
--- a/arch/x86/boot/compressed/head_32.S +++ b/arch/x86/boot/compressed/head_32.S @@ -187,7 +187,7 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated leal boot_heap@GOTOFF(%ebx), %eax pushl %eax /* heap area */ pushl %esi /* real mode pointer */
- call extract_kernel /* returns kernel location in %eax */
- call extract_kernel /* returns kernel entry point in %eax */ addl $24, %esp
/* --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -580,7 +580,7 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated movl input_len(%rip), %ecx /* input_len */ movq %rbp, %r8 /* output target address */ movl output_len(%rip), %r9d /* decompressed length, end of relocs */
- call extract_kernel /* returns kernel location in %rax */
- call extract_kernel /* returns kernel entry point in %rax */ popq %rsi
/* --- a/arch/x86/boot/compressed/misc.c +++ b/arch/x86/boot/compressed/misc.c @@ -277,7 +277,7 @@ static inline void handle_relocations(vo { } #endif
-static void parse_elf(void *output) +static size_t parse_elf(void *output) { #ifdef CONFIG_X86_64 Elf64_Ehdr ehdr; @@ -293,10 +293,8 @@ static void parse_elf(void *output) if (ehdr.e_ident[EI_MAG0] != ELFMAG0 || ehdr.e_ident[EI_MAG1] != ELFMAG1 || ehdr.e_ident[EI_MAG2] != ELFMAG2 ||
ehdr.e_ident[EI_MAG3] != ELFMAG3) {
ehdr.e_ident[EI_MAG3] != ELFMAG3)
return;}
debug_putstr("Parsing ELF... ");
@@ -328,6 +326,8 @@ static void parse_elf(void *output) }
free(phdrs);
- return ehdr.e_entry - LOAD_PHYSICAL_ADDR;
}
/* @@ -356,6 +356,7 @@ asmlinkage __visible void *extract_kerne const unsigned long kernel_total_size = VO__end - VO__text; unsigned long virt_addr = LOAD_PHYSICAL_ADDR; unsigned long needed_size;
size_t entry_offset;
/* Retain x86 boot parameters pointer passed from startup_32/64. */ boot_params = rmode;
@@ -456,14 +457,17 @@ asmlinkage __visible void *extract_kerne debug_putstr("\nDecompressing Linux... "); __decompress(input_data, input_len, NULL, NULL, output, output_len, NULL, error);
- parse_elf(output);
- entry_offset = parse_elf(output); handle_relocations(output, output_len, virt_addr);
- debug_putstr("done.\nBooting the kernel.\n");
debug_putstr("done.\nBooting the kernel (entry_offset: 0x");
debug_puthex(entry_offset);
debug_putstr(").\n");
/* Disable exception handling before booting the kernel */ cleanup_exception_handling();
- return output;
- return output + entry_offset;
}
void fortify_panic(const char *name)
I would be surprised if this *didn't* break some boot loader. ..