Commit-ID: 93a209aaaad495d7d0bc9b6186a4495934f70402 Gitweb: https://git.kernel.org/tip/93a209aaaad495d7d0bc9b6186a4495934f70402 Author: Chao Fan <fanc.f...@cn.fujitsu.com> AuthorDate: Wed, 23 Jan 2019 19:08:47 +0800 Committer: Borislav Petkov <b...@suse.de> CommitDate: Fri, 1 Feb 2019 11:52:55 +0100
x86/boot: Search for RSDP in memory Scan memory (EBDA) for the RSDP and verify RSDP by signature and checksum. [ bp: - Trim commit message. - Simplify bios_get_rsdp_addr() and cleanup mad casting. ] Signed-off-by: Chao Fan <fanc.f...@cn.fujitsu.com> Signed-off-by: Borislav Petkov <b...@suse.de> Cc: b...@redhat.com Cc: caoj.f...@cn.fujitsu.com Cc: "H. Peter Anvin" <h...@zytor.com> Cc: indou.ta...@jp.fujitsu.com Cc: Ingo Molnar <mi...@redhat.com> Cc: kas...@redhat.com Cc: Kees Cook <keesc...@chromium.org> Cc: msys.miz...@gmail.com Cc: Thomas Gleixner <t...@linutronix.de> Cc: x86-ml <x...@kernel.org> Link: https://lkml.kernel.org/r/20190123110850.12433-5-fanc.f...@cn.fujitsu.com --- arch/x86/boot/compressed/acpi.c | 77 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 77 insertions(+) diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c index 5559fde1c0fe..66bda1b5cf94 100644 --- a/arch/x86/boot/compressed/acpi.c +++ b/arch/x86/boot/compressed/acpi.c @@ -107,3 +107,80 @@ static acpi_physical_address efi_get_rsdp_addr(void) #endif return rsdp_addr; } + +static u8 compute_checksum(u8 *buffer, u32 length) +{ + u8 *end = buffer + length; + u8 sum = 0; + + while (buffer < end) + sum += *(buffer++); + + return sum; +} + +/* Search a block of memory for the RSDP signature. */ +static u8 *scan_mem_for_rsdp(u8 *start, u32 length) +{ + struct acpi_table_rsdp *rsdp; + u8 *address, *end; + + end = start + length; + + /* Search from given start address for the requested length */ + for (address = start; address < end; address += ACPI_RSDP_SCAN_STEP) { + /* + * Both RSDP signature and checksum must be correct. + * Note: Sometimes there exists more than one RSDP in memory; + * the valid RSDP has a valid checksum, all others have an + * invalid checksum. + */ + rsdp = (struct acpi_table_rsdp *)address; + + /* BAD Signature */ + if (!ACPI_VALIDATE_RSDP_SIG(rsdp->signature)) + continue; + + /* Check the standard checksum */ + if (compute_checksum((u8 *)rsdp, ACPI_RSDP_CHECKSUM_LENGTH)) + continue; + + /* Check extended checksum if table version >= 2 */ + if ((rsdp->revision >= 2) && + (compute_checksum((u8 *)rsdp, ACPI_RSDP_XCHECKSUM_LENGTH))) + continue; + + /* Signature and checksum valid, we have found a real RSDP */ + return address; + } + return NULL; +} + +/* Search RSDP address in EBDA. */ +static acpi_physical_address bios_get_rsdp_addr(void) +{ + unsigned long address; + u8 *rsdp; + + /* Get the location of the Extended BIOS Data Area (EBDA) */ + address = *(u16 *)ACPI_EBDA_PTR_LOCATION; + address <<= 4; + + /* + * Search EBDA paragraphs (EBDA is required to be a minimum of + * 1K length) + */ + if (address > 0x400) { + rsdp = scan_mem_for_rsdp((u8 *)address, ACPI_EBDA_WINDOW_SIZE); + if (rsdp) + return (acpi_physical_address)(unsigned long)rsdp; + } + + /* Search upper memory: 16-byte boundaries in E0000h-FFFFFh */ + rsdp = scan_mem_for_rsdp((u8 *) ACPI_HI_RSDP_WINDOW_BASE, + ACPI_HI_RSDP_WINDOW_SIZE); + if (rsdp) + return (acpi_physical_address)(unsigned long)rsdp; + + return 0; +}
