linux-kernel - Re: [PATCH v1 1/3] objtool/LoongArch: Fix fall through warning about efi_boot

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250901081616.GA4067720@noisy.programming.kicks-ass.net>
Date: Mon, 1 Sep 2025 10:16:16 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Huacai Chen <chenhuacai@...nel.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>, loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/3] objtool/LoongArch: Fix fall through warning about
 efi_boot_kernel()

On Mon, Sep 01, 2025 at 03:21:54PM +0800, Tiezhu Yang wrote:
> When compiling with LLVM and CONFIG_LTO_CLANG is set, there exists
> the following objtool warning:
> 
>   vmlinux.o: warning: objtool: __efistub_efi_boot_kernel()
>   falls through to next function __efistub_exit_boot_func()
> 
> This is because efi_boot_kernel() doesn't end with a return instruction
> or an unconditional jump, then objtool has determined that the function
> can fall through into the next function.
> 
> At the beginning, try to do something to make efi_boot_kernel() ends with
> an unconditional jump instruction, but it is not a proper way.
> 
> After more analysis, one simple way is to ignore these EFISTUB functions
> in validate_branch() of objtool since they are useless for stack unwinder.
> 

This is drivers/firmware/efi/libstub/loongarch.c:efi_boot_kernel(),
right?

Why not simply do something like:

diff --git a/drivers/firmware/efi/libstub/loongarch.c b/drivers/firmware/efi/libstub/loongarch.c
index 3782d0a187d1..082611a5f1f0 100644
--- a/drivers/firmware/efi/libstub/loongarch.c
+++ b/drivers/firmware/efi/libstub/loongarch.c
@@ -81,4 +81,5 @@ efi_status_t efi_boot_kernel(void *handle, efi_loaded_image_t *image,
 
 	real_kernel_entry(true, (unsigned long)cmdline_ptr,
 			  (unsigned long)efi_system_table);
+	BUG();
 }