linux-hardening - Re: [PATCH] ARM: socfpga: Fix crash with CONFIG_FORTIRY

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Date:   Wed, 17 Nov 2021 14:01:50 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Dinh Nguyen <dinguyen@...nel.org>,
        "Ivan T . Ivanov" <iivanov@...e.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ARM: socfpga: Fix crash with CONFIG_FORTIRY_SOURCE

On Wed, Nov 17, 2021 at 08:32:44PM +0100, Takashi Iwai wrote:
> When CONFIG_FORTIFY_SOURCE is set, memcpy() checks the potential
> buffer overflow and panics.  The code in sofcpga bootstrapping
> contains the memcpy() calls are mistakenly translated as the shorter
> size, hence it triggers a panic as if it were overflowing.
> 
> This patch adds the __NO_FORTIFY define for avoiding the
> false-positive crash.
> 
> Buglink: https://bugzilla.suse.com/show_bug.cgi?id=1192473
> Signed-off-by: Takashi Iwai <tiwai@...e.de>
> ---
> 
> I took an easier path for now, as the attempt with a foced cast
> failed.  If there is a better way to handle, let me know, I'd happily
> resubmit.  Thanks!
> 

The way these have been fixed in the past is to declare these as char
arrays (see include/asm-generic/sections.h). I'd prefer something like
this (totally untested):

diff --git a/arch/arm/mach-socfpga/core.h b/arch/arm/mach-socfpga/core.h
index fc2608b18a0d..18f01190dcfd 100644
--- a/arch/arm/mach-socfpga/core.h
+++ b/arch/arm/mach-socfpga/core.h
@@ -33,7 +33,7 @@ extern void __iomem *sdr_ctl_base_addr;
 u32 socfpga_sdram_self_refresh(u32 sdr_base);
 extern unsigned int socfpga_sdram_self_refresh_sz;
 
-extern char secondary_trampoline, secondary_trampoline_end;
+extern char secondary_trampoline[], secondary_trampoline_end[];
 
 extern unsigned long socfpga_cpu1start_addr;
 
diff --git a/arch/arm/mach-socfpga/platsmp.c b/arch/arm/mach-socfpga/platsmp.c
index fbb80b883e5d..201191cf68f3 100644
--- a/arch/arm/mach-socfpga/platsmp.c
+++ b/arch/arm/mach-socfpga/platsmp.c
@@ -20,14 +20,14 @@
 
 static int socfpga_boot_secondary(unsigned int cpu, struct task_struct *idle)
 {
-	int trampoline_size = &secondary_trampoline_end - &secondary_trampoline;
+	int trampoline_size = secondary_trampoline_end - secondary_trampoline;
 
 	if (socfpga_cpu1start_addr) {
 		/* This will put CPU #1 into reset. */
 		writel(RSTMGR_MPUMODRST_CPU1,
 		       rst_manager_base_addr + SOCFPGA_RSTMGR_MODMPURST);
 
-		memcpy(phys_to_virt(0), &secondary_trampoline, trampoline_size);
+		memcpy(phys_to_virt(0), secondary_trampoline, trampoline_size);
 
 		writel(__pa_symbol(secondary_startup),
 		       sys_manager_base_addr + (socfpga_cpu1start_addr & 0x000000ff));
@@ -45,12 +45,12 @@ static int socfpga_boot_secondary(unsigned int cpu, struct task_struct *idle)
 
 static int socfpga_a10_boot_secondary(unsigned int cpu, struct task_struct *idle)
 {
-	int trampoline_size = &secondary_trampoline_end - &secondary_trampoline;
+	int trampoline_size = secondary_trampoline_end - secondary_trampoline;
 
 	if (socfpga_cpu1start_addr) {
 		writel(RSTMGR_MPUMODRST_CPU1, rst_manager_base_addr +
 		       SOCFPGA_A10_RSTMGR_MODMPURST);
-		memcpy(phys_to_virt(0), &secondary_trampoline, trampoline_size);
+		memcpy(phys_to_virt(0), secondary_trampoline, trampoline_size);
 
 		writel(__pa_symbol(secondary_startup),
 		       sys_manager_base_addr + (socfpga_cpu1start_addr & 0x00000fff));

>  arch/arm/mach-socfpga/platsmp.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm/mach-socfpga/platsmp.c b/arch/arm/mach-socfpga/platsmp.c
> index fbb80b883e5d..d46b1af96a8a 100644
> --- a/arch/arm/mach-socfpga/platsmp.c
> +++ b/arch/arm/mach-socfpga/platsmp.c
> @@ -5,6 +5,9 @@
>   * Based on platsmp.c, Copyright (C) 2002 ARM Ltd.
>   * Copyright (C) 2012 Altera Corporation
>   */
> +
> +#define __NO_FORTIFY /* need to avoid the crash with memcpy() calls */
> +
>  #include <linux/delay.h>
>  #include <linux/init.h>
>  #include <linux/smp.h>
> -- 
> 2.26.2
> 

-- 
Kees Cook