linux-kernel - [PATCH 01/11] x86: compressed: avoid gcc-11 -Wstringop-overread warning

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Date:   Mon, 22 Mar 2021 17:02:39 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     linux-kernel@...r.kernel.org, Martin Sebor <msebor@....gnu.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org
Cc:     Arnd Bergmann <arnd@...db.de>, Ning Sun <ning.sun@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Simon Kelley <simon@...kelleys.org.uk>,
        James Smart <james.smart@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Anders Larsen <al@...rsen.net>, Tejun Heo <tj@...nel.org>,
        Serge Hallyn <serge@...lyn.com>,
        Imre Deak <imre.deak@...el.com>,
        linux-arm-kernel@...ts.infradead.org,
        tboot-devel@...ts.sourceforge.net, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, ath11k@...ts.infradead.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-scsi@...r.kernel.org, cgroups@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        "H. Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>
Subject: [PATCH 01/11] x86: compressed: avoid gcc-11 -Wstringop-overread warning

From: Arnd Bergmann <arnd@...db.de>

gcc gets confused by the comparison of a pointer to an integer listeral,
with the assumption that this is an offset from a NULL pointer and that
dereferencing it is invalid:

In file included from arch/x86/boot/compressed/misc.c:18:
In function ‘parse_elf’,
    inlined from ‘extract_kernel’ at arch/x86/boot/compressed/misc.c:442:2:
arch/x86/boot/compressed/../string.h:15:23: error: ‘__builtin_memcpy’ reading 64 bytes from a region of size 0 [-Werror=stringop-overread]
   15 | #define memcpy(d,s,l) __builtin_memcpy(d,s,l)
      |                       ^~~~~~~~~~~~~~~~~~~~~~~
arch/x86/boot/compressed/misc.c:283:9: note: in expansion of macro ‘memcpy’
  283 |         memcpy(&ehdr, output, sizeof(ehdr));
      |         ^~~~~~

I could not find any good workaround for this, but as this is only
a warning for a failure during early boot, removing the line entirely
works around the warning.

This should probably get addressed in gcc instead, before 11.1 gets
released.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/x86/boot/compressed/misc.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 3a214cc3239f..9ada64e66cb7 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -430,8 +430,6 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 		error("Destination address too large");
 #endif
 #ifndef CONFIG_RELOCATABLE
-	if ((unsigned long)output != LOAD_PHYSICAL_ADDR)
-		error("Destination address does not match LOAD_PHYSICAL_ADDR");
 	if (virt_addr != LOAD_PHYSICAL_ADDR)
 		error("Destination virtual address changed when not relocatable");
 #endif
-- 
2.29.2