From 2e604c0f19dcdd433b3863ffc3da9bc0787ca765 Mon Sep 17 00:00:00 2001 From: Josh Boyer Date: Wed, 6 Mar 2013 20:23:30 -0800 Subject: x86: Don't clear efi_info even if the sentinel hits When boot_params->sentinel is set, all we really know is that some undefined set of fields in struct boot_params contain garbage. In the particular case of efi_info, however, there is a private magic for that substructure, so it is generally safe to leave it even if the bootloader is broken. kexec (for which we did the initial analysis) did not initialize this field, but of course all the EFI bootloaders do, and most EFI bootloaders are broken in this respect (and should be fixed.) Reported-by: Robin Holt Link: http://lkml.kernel.org/r/CA%2B5PVA51-FT14p4CRYKbicykugVb=PiaEycdQ57CK2km_OQuRQ@mail.gmail.com Tested-by: Josh Boyer Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/bootparam_utils.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'arch/x86/include/asm/bootparam_utils.h') diff --git a/arch/x86/include/asm/bootparam_utils.h b/arch/x86/include/asm/bootparam_utils.h index 5b5e9cb774b5..ff808ef4fdb4 100644 --- a/arch/x86/include/asm/bootparam_utils.h +++ b/arch/x86/include/asm/bootparam_utils.h @@ -14,13 +14,15 @@ * analysis of kexec-tools; if other broken bootloaders initialize a * different set of fields we will need to figure out how to disambiguate. * + * Note: efi_info is commonly left uninitialized, but that field has a + * private magic, so it is better to leave it unchanged. */ static void sanitize_boot_params(struct boot_params *boot_params) { if (boot_params->sentinel) { /*fields in boot_params are not valid, clear them */ memset(&boot_params->olpc_ofw_header, 0, - (char *)&boot_params->alt_mem_k - + (char *)&boot_params->efi_info - (char *)&boot_params->olpc_ofw_header); memset(&boot_params->kbd_status, 0, (char *)&boot_params->hdr - -- cgit v1.2.3 From 3c4aff6b9a183b4f24eb7b8dd6c8a92cdba3bc75 Mon Sep 17 00:00:00 2001 From: Peter Jones Date: Wed, 6 Mar 2013 13:00:23 -0500 Subject: x86, doc: Be explicit about what the x86 struct boot_params requires If the sentinel triggers, we do not want the boot loader authors to just poke it and make the error go away, we want them to actually fix the problem. This should help avoid making the incorrect change in non-compliant bootloaders. [ hpa: dropped the Documentation/x86/boot.txt hunk pending clarifications ] Signed-off-by: Peter Jones Link: http://lkml.kernel.org/r/1362592823-28967-1-git-send-email-pjones@redhat.com Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/bootparam_utils.h | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) (limited to 'arch/x86/include/asm/bootparam_utils.h') diff --git a/arch/x86/include/asm/bootparam_utils.h b/arch/x86/include/asm/bootparam_utils.h index ff808ef4fdb4..653668d140f9 100644 --- a/arch/x86/include/asm/bootparam_utils.h +++ b/arch/x86/include/asm/bootparam_utils.h @@ -19,8 +19,22 @@ */ static void sanitize_boot_params(struct boot_params *boot_params) { + /* + * IMPORTANT NOTE TO BOOTLOADER AUTHORS: do not simply clear + * this field. The purpose of this field is to guarantee + * compliance with the x86 boot spec located in + * Documentation/x86/boot.txt . That spec says that the + * *whole* structure should be cleared, after which only the + * portion defined by struct setup_header (boot_params->hdr) + * should be copied in. + * + * If you're having an issue because the sentinel is set, you + * need to change the whole structure to be cleared, not this + * (or any other) individual field, or you will soon have + * problems again. + */ if (boot_params->sentinel) { - /*fields in boot_params are not valid, clear them */ + /* fields in boot_params are left uninitialized, clear them */ memset(&boot_params->olpc_ofw_header, 0, (char *)&boot_params->efi_info - (char *)&boot_params->olpc_ofw_header); -- cgit v1.2.3