cbfstool/linux_trampoline: Fill the ACPI RSDP entry

With LinuxBoot Linux relied on the legacy method of fetching the RSDP
pointer to get ACPI. This uses a more modern approach available since
2018 on the Linux kernel, which involves filling in the zero page.

This method takes precedence over any other method of fetching the
RSDP in Linux (UEFI, Kexec, Legacy/BIOS). Some UEFI zealots are
threatening that legacy code will be removed from Linux so it's best
to already adapt to that possibility.

Tested on Qemu:
- With qemu the RSDP is always in the EBDA, so checking if Linux uses
  the provided pointer is better done with a forced bad entry
- With a fake bad pointer Linux correctly does not find RDSP

Change-Id: I688b94608b03b0177c42d2834c7e3beb802ae686
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62574
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

2 files changed, 22 insertions, 9 deletions

diff --git a/util/cbfstool/linux_trampoline.S b/util/cbfstool/linux_trampoline.S
index 726852804f..767c8bebd3 100644
--- a/util/cbfstool/linux_trampoline.S
+++ b/util/cbfstool/linux_trampoline.S
@@ -13,7 +13,9 @@
 #define CB_TAG_FORWARD 0x11
 #define CB_TAG_MEMORY 0x1
 #define CB_TAG_FRAMEBUFFER 0x12
+#define CB_TAG_ACPI_RSDP 0x43
 
+#define ACPI_RSDP_ADDR 0x70
 #define E820_NR_OFFSET 0x1e8
 #define LINUX_ENTRY_OFFSET 0x214
 #define E820_OFFSET 0x2d0
@@ -52,7 +54,7 @@ jmp .headerSearch
 
 .testMemory:
 cmp $CB_TAG_MEMORY, (%ebx)
-jne .testFramebuffer
+jne .testAcpiRsdp
 
 /* memory tag: copy e820 map and entry count. also determine alt_mem_k */
 mov 4(%ebx), %eax
@@ -87,6 +89,16 @@ dec %eax
 add $20, %edi
 jmp .test_e820_entry
 
+.testAcpiRsdp:
+cmp $CB_TAG_ACPI_RSDP, (%ebx)
+jne .testFramebuffer
+
+mov 8(%ebx), %eax
+mov %eax, (LINUX_PARAM_LOC + ACPI_RSDP_ADDR)
+mov 12(%ebx), %eax
+mov %eax, (LINUX_PARAM_LOC + ACPI_RSDP_ADDR + 4)
+jmp .endScan
+
 .testFramebuffer:
 cmp $CB_TAG_FRAMEBUFFER, (%ebx)
 jne .endScan
diff --git a/util/cbfstool/linux_trampoline.c b/util/cbfstool/linux_trampoline.c
index b804c80542..46bb800ad6 100644
--- a/util/cbfstool/linux_trampoline.c
+++ b/util/cbfstool/linux_trampoline.c
@@ -3,17 +3,18 @@
 unsigned char trampoline[] = {
   0xfc, 0x31, 0xd2, 0xb9, 0x00, 0x00, 0x00, 0x00, 0xbb, 0x00, 0x00, 0x01, 0x00, 0x01, 0xcb, 0x8b,
   0x01, 0x3d, 0x4c, 0x42, 0x49, 0x4f, 0x74, 0x07, 0x83, 0xc1, 0x10, 0x39, 0xcb, 0x75, 0xe9, 0x39,
-  0xcb, 0x0f, 0x84, 0xaa, 0x00, 0x00, 0x00, 0x8b, 0x59, 0x04, 0x01, 0xcb, 0x8b, 0x49, 0x14, 0x83,
+  0xcb, 0x0f, 0x84, 0xc5, 0x00, 0x00, 0x00, 0x8b, 0x59, 0x04, 0x01, 0xcb, 0x8b, 0x49, 0x14, 0x83,
   0x3b, 0x11, 0x75, 0x05, 0x8b, 0x4b, 0x08, 0xeb, 0xcf, 0x83, 0x3b, 0x01, 0x75, 0x53, 0x8b, 0x43,
   0x04, 0x83, 0xe8, 0x08, 0xc1, 0xe8, 0x02, 0x3d, 0xa0, 0x00, 0x00, 0x00, 0x7e, 0x05, 0xb8, 0xa0,
   0x00, 0x00, 0x00, 0x89, 0xc6, 0xbf, 0x05, 0x00, 0x00, 0x00, 0xf7, 0xf7, 0xa3, 0xe8, 0x01, 0x09,
   0x00, 0x89, 0xf0, 0x91, 0x8d, 0x73, 0x08, 0xbf, 0xd0, 0x02, 0x09, 0x00, 0xf3, 0xa5, 0x91, 0xa1,
-  0xe8, 0x01, 0x09, 0x00, 0xbf, 0xd0, 0x02, 0x09, 0x00, 0x83, 0xf8, 0x00, 0x74, 0x18, 0x83, 0x7f,
+  0xe8, 0x01, 0x09, 0x00, 0xbf, 0xd0, 0x02, 0x09, 0x00, 0x83, 0xf8, 0x00, 0x74, 0x2f, 0x83, 0x7f,
   0x10, 0x0c, 0x7e, 0x07, 0xc7, 0x47, 0x10, 0x02, 0x00, 0x00, 0x00, 0x48, 0x83, 0xc7, 0x14, 0xeb,
-  0xe8, 0x83, 0x3b, 0x12, 0x75, 0x00, 0x03, 0x5b, 0x04, 0x49, 0x75, 0x93, 0xb8, 0x00, 0x00, 0x04,
-  0x00, 0xc7, 0x40, 0x10, 0xff, 0xff, 0x00, 0x00, 0xc7, 0x40, 0x14, 0x00, 0x9b, 0xcf, 0x00, 0xc7,
-  0x40, 0x18, 0xff, 0xff, 0x00, 0x00, 0xc7, 0x40, 0x1c, 0x00, 0x93, 0xcf, 0x00, 0xc6, 0x00, 0x2b,
-  0x89, 0x40, 0x02, 0x0f, 0x01, 0x10, 0xbe, 0x00, 0x00, 0x09, 0x00, 0xff, 0x25, 0x14, 0x02, 0x09,
-  0x00, 0xf4, 0xeb, 0xfd
+  0xe8, 0x83, 0x3b, 0x43, 0x75, 0x12, 0x8b, 0x43, 0x08, 0xa3, 0x70, 0x00, 0x09, 0x00, 0x8b, 0x43,
+  0x0c, 0xa3, 0x74, 0x00, 0x09, 0x00, 0xeb, 0x05, 0x83, 0x3b, 0x12, 0x75, 0x00, 0x03, 0x5b, 0x04,
+  0x49, 0x0f, 0x85, 0x78, 0xff, 0xff, 0xff, 0xb8, 0x00, 0x00, 0x04, 0x00, 0xc7, 0x40, 0x10, 0xff,
+  0xff, 0x00, 0x00, 0xc7, 0x40, 0x14, 0x00, 0x9b, 0xcf, 0x00, 0xc7, 0x40, 0x18, 0xff, 0xff, 0x00,
+  0x00, 0xc7, 0x40, 0x1c, 0x00, 0x93, 0xcf, 0x00, 0xc6, 0x00, 0x2b, 0x89, 0x40, 0x02, 0x0f, 0x01,
+  0x10, 0xbe, 0x00, 0x00, 0x09, 0x00, 0xff, 0x25, 0x14, 0x02, 0x09, 0x00, 0xf4, 0xeb, 0xfd
 };
-unsigned int trampoline_len = 212;
+unsigned int trampoline_len = 239;