linux-kernel - Re: [PATCH] arm64: module: PLT allowed even !RANDOM

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Message-Id: <56c2d30b-2f25-4613-aab1-00fccbd2fa05@app.fastmail.com>
Date:   Mon, 23 Oct 2023 10:08:33 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Maria Yu" <quic_aiquny@...cinc.com>,
        "Catalin Marinas" <catalin.marinas@....com>,
        "Will Deacon" <will@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...cinc.com, linux-arm-msm@...r.kernel.org,
        "Ard Biesheuvel" <ardb@...nel.org>
Subject: Re: [PATCH] arm64: module: PLT allowed even !RANDOM_BASE

On Mon, Oct 23, 2023, at 09:57, Maria Yu wrote:
> Module PLT feature can be enabled even when RANDOM_BASE is disabled.
> Break BLT entry counts of relocation types will make module plt entry
> allocation fail and finally exec format error for even correct and plt
> allocation available modules.
>
> Signed-off-by: Maria Yu <quic_aiquny@...cinc.com>

Adding Ard Biesheuvel to Cc, as he added the check in commit
a257e02579e42 ("arm64/kernel: don't ban ADRP to work around
Cortex-A53 erratum #843419")

>  arch/arm64/kernel/module-plts.c | 3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/module-plts.c 
> b/arch/arm64/kernel/module-plts.c
> index bd69a4e7cd60..21a67d52d7a0 100644
> --- a/arch/arm64/kernel/module-plts.c
> +++ b/arch/arm64/kernel/module-plts.c
> @@ -167,9 +167,6 @@ static unsigned int count_plts(Elf64_Sym *syms, 
> Elf64_Rela *rela, int num,
>  		switch (ELF64_R_TYPE(rela[i].r_info)) {
>  		case R_AARCH64_JUMP26:
>  		case R_AARCH64_CALL26:
> -			if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
> -				break;
> -
>  			/*
>  			 * We only have to consider branch targets that resolve
>  			 * to symbols that are defined in a different section.

I see there are two such checks (in partition_branch_plt_relas()
and in count_plts()), can you explain in more detail how you
concluded that one of them is correct but the other one is not?

     Arnd