linux-kernel - [tip: x86/paravirt] x86/paravirt: Ensure proper alignment

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Date:   Wed, 21 Sep 2022 11:08:44 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>, Juergen Gross <jgross@...e.com>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/paravirt] x86/paravirt: Ensure proper alignment

The following commit has been merged into the x86/paravirt branch of tip:

Commit-ID:     f92ff8f5dca2acfa475842c71212657b0703c3be
Gitweb:        https://git.kernel.org/tip/f92ff8f5dca2acfa475842c71212657b0703c3be
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Thu, 15 Sep 2022 13:10:40 +02:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Wed, 21 Sep 2022 12:30:16 +02:00

x86/paravirt: Ensure proper alignment

The entries in the .parainstructions sections are 8 byte aligned and the
corresponding C struct paravirt_patch_site makes the array offset 16
bytes.

Though the pushed entries are only using 12 bytes, __parainstructions_end
is therefore 4 bytes short.

That works by chance because it's only used in a loop:

     for (p = start; p < end; p++)

But this falls flat when calculating the number of elements:

    n = end - start

That's obviously off by one.

Ensure that the gap is filled and the last entry is occupying 16 bytes.

  [ bp: Add the proper struct and section names. ]

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Juergen Gross <jgross@...e.com>
Link: https://lore.kernel.org/r/20220915111142.992398801@infradead.org
---
 arch/x86/include/asm/paravirt.h       | 1 +
 arch/x86/include/asm/paravirt_types.h | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 964442b..2a0b8dd 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -743,6 +743,7 @@ extern void default_banner(void);
 	 word 771b;				\
 	 .byte ptype;				\
 	 .byte 772b-771b;			\
+	 _ASM_ALIGN;				\
 	.popsection
 
 
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 89df6c6..27b036a 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -294,6 +294,7 @@ extern struct paravirt_patch_template pv_ops;
 	"  .byte " type "\n"				\
 	"  .byte 772b-771b\n"				\
 	"  .short " clobber "\n"			\
+	_ASM_ALIGN "\n"					\
 	".popsection\n"
 
 /* Generate patchable code, with the default asm parameters. */