Commit-ID: 93a209aaaad495d7d0bc9b6186a4495934f70402
Gitweb: https://git.kernel.org/tip/93a209aaaad495d7d0bc9b6186a4495934f70402
Author: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx>
AuthorDate: Wed, 23 Jan 2019 19:08:47 +0800
Committer: Borislav Petkov <bp@xxxxxxx>
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.fnst@xxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: bhe@xxxxxxxxxx
Cc: caoj.fnst@xxxxxxxxxxxxxx
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: indou.takao@xxxxxxxxxxxxxx
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: kasong@xxxxxxxxxx
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: msys.mizuma@xxxxxxxxx
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190123110850.12433-5-fanc.fnst@xxxxxxxxxxxxxx
---
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;
+}
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