linux-kernel - Re: [PATCH v2] arm64: module: PLT allowed even !RANDOM

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Message-ID: <ZTeY0oBH3P22yOqA@FVFF77S0Q05N>
Date:   Tue, 24 Oct 2023 11:13:47 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Maria Yu <quic_aiquny@...cinc.com>
Cc:     catalin.marinas@....com, will@...nel.org, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...cinc.com, linux-arm-msm@...r.kernel.org, ardb@...nel.org
Subject: Re: [PATCH v2] arm64: module: PLT allowed even !RANDOM_BASE

On Tue, Oct 24, 2023 at 09:09:54AM +0800, 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.

The patch itself looks good; it would be better if we could make the commit
message explicit that this is a fix. Could we please replace that with:

| arm64: module: fix PLT counting when CONFIG_RANDOMIZE_BASE=n
| 
| The counting of module PLTs has been broken when CONFIG_RANDOMIZE_BASE=n
| since commit:
| 
|   3e35d303ab7d22c4 ("arm64: module: rework module VA range selection")
| 
| Prior to that commit, when CONFIG_RANDOMIZE_BASE=n, the kernel image and
| all modules were placed within a 128M region, and no PLTs were necessary
| for B or BL. Hence count_plts() and partition_branch_plt_relas() skipped
| handling B and BL when CONFIG_RANDOMIZE_BASE=n.
| 
| After that commit, modules can be placed anywhere within a 2G window
| regardless of CONFIG_RANDOMIZE_BASE, and hence PLTs may be necessary for
| B and BL even when CONFIG_RANDOMIZE_BASE=n. Unfortunately that commit
| failed to update count_plts() and partition_branch_plt_relas()
| accordingly.
| 
| Due to this, module_emit_plt_entry() may fail if an insufficient number
| of PLT entries have been reserved, resulting in modules failing to load
| with -ENOEXEC.
|
| Fix this by counting PLTs regardless of CONFIG_RANDOMIZE_BASE in 
| count_plts() and partition_branch_plt_relas().

... and add a fixes tag:

Fixes: 3e35d303ab7d22c4 ("arm64: module: rework module VA range selection")

With that:

Reviewed-by: Mark Rutland <mark.rutland@....com>

Mark.

> 
> Signed-off-by: Maria Yu <quic_aiquny@...cinc.com>
> ---
>  arch/arm64/kernel/module-plts.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c
> index bd69a4e7cd60..79200f21e123 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.
> @@ -269,9 +266,6 @@ static int partition_branch_plt_relas(Elf64_Sym *syms, Elf64_Rela *rela,
>  {
>  	int i = 0, j = numrels - 1;
>  
> -	if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
> -		return 0;
> -
>  	while (i < j) {
>  		if (branch_rela_needs_plt(syms, &rela[i], dstidx))
>  			i++;
> 
> base-commit: 05d3ef8bba77c1b5f98d941d8b2d4aeab8118ef1
> -- 
> 2.17.1
>