All of lore.kernel.org
 help / color / mirror / Atom feed
From: D Scott Phillips <scott@os.amperecomputing.com>
To: linux-arm-kernel@lists.infradead.org
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, James Morse <james.morse@arm.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Darren Hart <darren@os.amperecomputing.com>,
	patches@amperecomputing.com
Subject: [PATCH v2] arm64: Fix bit-shifting UB in the MIDR_CPU_MODEL() macro
Date: Wed,  2 Nov 2022 09:01:06 -0700	[thread overview]
Message-ID: <20221102160106.1096948-1-scott@os.amperecomputing.com> (raw)

CONFIG_UBSAN_SHIFT with gcc-5 complains that the shifting of
ARM_CPU_IMP_AMPERE (0xC0) into bits [31:24] by MIDR_CPU_MODEL() is
undefined behavior. Well, sort of, it actually spells the error as:

 arch/arm64/kernel/proton-pack.c: In function 'spectre_bhb_loop_affected':
 arch/arm64/include/asm/cputype.h:44:2: error: initializer element is not constant
   (((imp)   << MIDR_IMPLEMENTOR_SHIFT) | \
   ^

This isn't an issue for other Implementor codes, as all the other codes
have zero in the top bit and so are representable as a signed int.

Cast the implementor code to unsigned in MIDR_CPU_MODEL to remove the
undefined behavior.

Fixes: 0e5d5ae837c8 ("arm64: Add AMPERE1 to the Spectre-BHB affected list")
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: D Scott Phillips <scott@os.amperecomputing.com>
---
Changes since v1 (https://lore.kernel.org/all/20221017210119.3581-1-scott@os.amperecomputing.com/):
- cast in MIDR_CPU_MODEL() instead of changing ARM_CPU_IMP_AMPERE

 arch/arm64/include/asm/cputype.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/cputype.h b/arch/arm64/include/asm/cputype.h
index abc418650fec..65e53ef5a396 100644
--- a/arch/arm64/include/asm/cputype.h
+++ b/arch/arm64/include/asm/cputype.h
@@ -41,7 +41,7 @@
 	(((midr) & MIDR_IMPLEMENTOR_MASK) >> MIDR_IMPLEMENTOR_SHIFT)
 
 #define MIDR_CPU_MODEL(imp, partnum) \
-	(((imp)			<< MIDR_IMPLEMENTOR_SHIFT) | \
+	((_AT(u32, imp)		<< MIDR_IMPLEMENTOR_SHIFT) | \
 	(0xf			<< MIDR_ARCHITECTURE_SHIFT) | \
 	((partnum)		<< MIDR_PARTNUM_SHIFT))
 
-- 
2.37.3


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

             reply	other threads:[~2022-11-02 16:02 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-02 16:01 D Scott Phillips [this message]
2022-11-09 10:26 ` [PATCH v2] arm64: Fix bit-shifting UB in the MIDR_CPU_MODEL() macro Catalin Marinas

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20221102160106.1096948-1-scott@os.amperecomputing.com \
    --to=scott@os.amperecomputing.com \
    --cc=catalin.marinas@arm.com \
    --cc=darren@os.amperecomputing.com \
    --cc=geert@linux-m68k.org \
    --cc=james.morse@arm.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=patches@amperecomputing.com \
    --cc=will@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.