Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Tue, 08 Aug 2023 08:44:06 -0000
From:   "tip-bot2 for Ard Biesheuvel" <tip-bot2@linutronix.de>
Sender: tip-bot2@linutronix.de
Reply-to: linux-kernel@vger.kernel.org
To:     linux-tip-commits@vger.kernel.org
Subject: [tip: x86/boot] x86/efistub: Branch straight to kernel entry point
 from C code
Cc:     Ard Biesheuvel <ardb@kernel.org>,
        "Borislav Petkov (AMD)" <bp@alien8.de>, x86@kernel.org,
        linux-kernel@vger.kernel.org
In-Reply-To: <20230807162720.545787-4-ardb@kernel.org>
References: <20230807162720.545787-4-ardb@kernel.org>
MIME-Version: 1.0
Message-ID: <169148424606.27769.13302670504473669940.tip-bot2@tip-bot2>
Robot-ID: <tip-bot2@linutronix.de>
Robot-Unsubscribe: Contact <mailto:tglx@linutronix.de> to get blacklisted from these emails
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Precedence: bulk

The following commit has been merged into the x86/boot branch of tip:

Commit-ID:     d2d7a54f69b67cd0a30e0ebb5307cb2de625baac
Gitweb:        https://git.kernel.org/tip/d2d7a54f69b67cd0a30e0ebb5307cb2de625baac
Author:        Ard Biesheuvel <ardb@kernel.org>
AuthorDate:    Mon, 07 Aug 2023 18:27:00 +02:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Mon, 07 Aug 2023 20:36:06 +02:00

x86/efistub: Branch straight to kernel entry point from C code

Instead of returning to the calling code in assembler that does nothing
more than perform an indirect call with the boot_params pointer in
register ESI/RSI, perform the jump directly from the EFI stub C code.
This will allow the asm entrypoint code to be dropped entirely in
subsequent patches.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230807162720.545787-4-ardb@kernel.org
---
 drivers/firmware/efi/libstub/x86-stub.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 220be75..40a10db 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -290,7 +290,7 @@ adjust_memory_range_protection(unsigned long start, unsigned long size)
 #define TRAMPOLINE_PLACEMENT_BASE ((128 - 8)*1024)
 #define TRAMPOLINE_PLACEMENT_SIZE (640*1024 - (128 - 8)*1024)
 
-void startup_32(struct boot_params *boot_params);
+extern const u8 startup_32[], startup_64[];
 
 static void
 setup_memory_protection(unsigned long image_base, unsigned long image_size)
@@ -803,10 +803,19 @@ static efi_status_t exit_boot(struct boot_params *boot_params, void *handle)
 	return EFI_SUCCESS;
 }
 
+static void __noreturn enter_kernel(unsigned long kernel_addr,
+				    struct boot_params *boot_params)
+{
+	/* enter decompressed kernel with boot_params pointer in RSI/ESI */
+	asm("jmp *%0"::"r"(kernel_addr), "S"(boot_params));
+
+	unreachable();
+}
+
 /*
- * On success, we return the address of startup_32, which has potentially been
- * relocated by efi_relocate_kernel.
- * On failure, we exit to the firmware via efi_exit instead of returning.
+ * On success, this routine will jump to the relocated image directly and never
+ * return.  On failure, it will exit to the firmware via efi_exit() instead of
+ * returning.
  */
 asmlinkage unsigned long efi_main(efi_handle_t handle,
 				  efi_system_table_t *sys_table_arg,
@@ -950,7 +959,10 @@ asmlinkage unsigned long efi_main(efi_handle_t handle,
 		goto fail;
 	}
 
-	return bzimage_addr;
+	if (IS_ENABLED(CONFIG_X86_64))
+		bzimage_addr += startup_64 - startup_32;
+
+	enter_kernel(bzimage_addr, boot_params);
 fail:
 	efi_err("efi_main() failed!\n");