From: David Woodhouse <[email protected]> Check for broken bootloaders jumping into the kernel image at 0x200, which was never a defined entry point. It was *always* broken for a 32-bit kernel, and there's no sane way to tell a 32-bit bzImage from a 64-bit one. (Anyone who suggests looking at the kernel_alignment field, go and stand in the naughty corner. Besides, the offending bootloaders *didn't* do this.)
Signed-off-by: David Woodhouse <[email protected]> --- arch/x86/boot/compressed/head_64.S | 49 +++++++++++++++++++++++--------------- arch/x86/kernel/setup.c | 6 +++++ 2 files changed, 36 insertions(+), 19 deletions(-) diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index f5d1aaa..a7d8b7e 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -185,27 +185,28 @@ no_longmode: #include "../../kernel/verify_cpu.S" /* - * Be careful here startup_64 needs to be at a predictable - * address so I can export it in an ELF header. Bootloaders - * should look at the ELF header to find this address, as - * it may change in the future. + * startup_64 was once here, and some very naughty bootloaders decided + * to jump directly to it despite the fact that it was clearly marked + * 'this may change' and in fact had already moved once without + * fanfare. And despite the fact that they were not even checking for + * 32-bit vs. 64-bit kernels, so they were just jumping right into + * the compressed payload when asked to boot the former! + * + * These bootloaders are so *egregiously* broken, and for 32-bit + * kernels they broken in the "it just crashes instead of booting" + * sense of the word rather than just the "you got away with it, but + * someone needs to be whipped for this" sense of the word. So we don't + * feel the need to pander to them and retroactively "define" the + * entry point to be at 0x200. But for a *little* while let's catch it + * and give a nasty warning message during boot that their bootloader + * needs to be updated. */ .code64 .org 0x200 -ENTRY(startup_64) - /* - * We come here either from startup_32 or directly from a - * 64bit bootloader. If we come here from a bootloader we depend on - * an identity mapped page table being provied that maps our - * entire text+data+bss and hopefully all of memory. - */ -#ifdef CONFIG_EFI_STUB - /* - * The entry point for the PE/COFF executable is efi_pe_entry, so - * only legacy boot loaders will execute this jmp. - */ + movl $0xbad10ad, %edx jmp preferred_addr +#ifdef CONFIG_EFI_STUB ENTRY(efi_pe_entry) mov %rcx, %rdi mov %rdx, %rsi @@ -234,12 +235,19 @@ ENTRY(efi_stub_entry) subq $3b, %rax subq BP_pref_address(%rsi), %rax add BP_code32_start(%esi), %eax - leaq preferred_addr(%rax), %rax + leaq startup_64(%rax), %rax jmp *%rax - -preferred_addr: #endif + /* + * We come here either from startup_32 or directly from a + * 64bit bootloader. If we come here from a bootloader we depend on + * an identity mapped page table being provied that maps our + * entire text+data+bss and hopefully all of memory. + */ +ENTRY(startup_64) + movl $0, %edx +preferred_addr: /* Setup data segments. */ xorl %eax, %eax movl %eax, %ds @@ -251,6 +259,9 @@ preferred_addr: movl $0x20, %eax ltr %ax + /* Store 'bad load' flag in BP */ + movl %edx, BP_scratch(%rsi) + /* * Compute the decompressed kernel start address. It is where * we were loaded at aligned to a 2M boundary. %rbp contains the diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c index 23ddd55..02ce7d9 100644 --- a/arch/x86/kernel/setup.c +++ b/arch/x86/kernel/setup.c @@ -1061,6 +1061,12 @@ void __init setup_arch(char **cmdline_p) efi_enabled = 0; } #endif +#ifdef CONFIG_X86_64 + if (boot_params.scratch == 0xbad10ad) { + WARN(1, "Broken bootloader jumped to wrong entry point in the kernel image. " + "Please update your bootloader or new kernels may not boot."); + } +#endif } #ifdef CONFIG_X86_32 -- 1.8.0.1 -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
