x86/efistub: Omit physical KASLR when memory reservations exist

JIRA: https://issues.redhat.com/browse/RHEL-83461

This patch is a backport of the following upstream commit:
commit 15aa8fb
Author: Ard Biesheuvel <ardb@kernel.org>
Date:   Thu May 16 11:05:42 2024 +0200

    x86/efistub: Omit physical KASLR when memory reservations exist

    The legacy decompressor has elaborate logic to ensure that the
    randomized physical placement of the decompressed kernel image does not
    conflict with any memory reservations, including ones specified on the
    command line using mem=, memmap=, efi_fake_mem= or hugepages=, which are
    taken into account by the kernel proper at a later stage.

    When booting in EFI mode, it is the firmware's job to ensure that the
    chosen range does not conflict with any memory reservations that it
    knows about, and this is trivially achieved by using the firmware's
    memory allocation APIs.

    That leaves reservations specified on the command line, though, which
    the firmware knows nothing about, as these regions have no other special
    significance to the platform. Since commit

      a1b87d5 ("x86/efistub: Avoid legacy decompressor when doing EFI boot")

    these reservations are not taken into account when randomizing the
    physical placement, which may result in conflicts where the memory
    cannot be reserved by the kernel proper because its own executable image
    resides there.

    To avoid having to duplicate or reuse the existing complicated logic,
    disable physical KASLR entirely when such overrides are specified. These
    are mostly diagnostic tools or niche features, and physical KASLR (as
    opposed to virtual KASLR, which is much more important as it affects the
    memory addresses observed by code executing in the kernel) is something
    we can live without.

    Closes: https://lkml.kernel.org/r/FA5F6719-8824-4B04-803E-82990E65E627%40akamai.com
    Reported-by: Ben Chaney <bchaney@akamai.com>
    Fixes: a1b87d5 ("x86/efistub: Avoid legacy decompressor when doing EFI boot")
    Cc:  <stable@vger.kernel.org> # v6.1+
    Reviewed-by: Kees Cook <keescook@chromium.org>
    Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Signed-off-by: Charles Haithcock <chaithco@redhat.com>

Author: chaithco

drivers/firmware/efi/libstub/x86-stub.c

@@ -770,6 +770,26 @@ static void error(char *str)
 	efi_warn("Decompression failed: %s\n", str);
 }
 
+static const char *cmdline_memmap_override;
+
+static efi_status_t parse_options(const char *cmdline)
+{
+	static const char opts[][14] = {
+		"mem=", "memmap=", "efi_fake_mem=", "hugepages="
+	};
+
+	for (int i = 0; i < ARRAY_SIZE(opts); i++) {
+		const char *p = strstr(cmdline, opts[i]);
+
+		if (p == cmdline || (p > cmdline && isspace(p[-1]))) {
+			cmdline_memmap_override = opts[i];
+			break;
+		}
+	}
+
+	return efi_parse_options(cmdline);
+}
+
 static efi_status_t efi_decompress_kernel(unsigned long *kernel_entry)
 {
 	unsigned long virt_addr = LOAD_PHYSICAL_ADDR;
@@ -801,6 +821,10 @@ static efi_status_t efi_decompress_kernel(unsigned long *kernel_entry)
 		    !memcmp(efistub_fw_vendor(), ami, sizeof(ami))) {
 			efi_debug("AMI firmware v2.0 or older detected - disabling physical KASLR\n");
 			seed[0] = 0;
+		} else if (cmdline_memmap_override) {
+			efi_info("%s detected on the kernel command line - disabling physical KASLR\n",
+				 cmdline_memmap_override);
+			seed[0] = 0;
 		}
 
 		boot_params_ptr->hdr.loadflags |= KASLR_FLAG;
@@ -877,7 +901,7 @@ void __noreturn efi_stub_entry(efi_handle_t handle,
 	}
 
 #ifdef CONFIG_CMDLINE_BOOL
-	status = efi_parse_options(CONFIG_CMDLINE);
+	status = parse_options(CONFIG_CMDLINE);
 	if (status != EFI_SUCCESS) {
 		efi_err("Failed to parse options\n");
 		goto fail;
@@ -886,7 +910,7 @@ void __noreturn efi_stub_entry(efi_handle_t handle,
 	if (!IS_ENABLED(CONFIG_CMDLINE_OVERRIDE)) {
 		unsigned long cmdline_paddr = ((u64)hdr->cmd_line_ptr |
 					       ((u64)boot_params->ext_cmd_line_ptr << 32));
-		status = efi_parse_options((char *)cmdline_paddr);
+		status = parse_options((char *)cmdline_paddr);
 		if (status != EFI_SUCCESS) {
 			efi_err("Failed to parse options\n");
 			goto fail;