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From:   Arvind Sankar <nivedita@alum.mit.edu>
To:     x86@kernel.org
Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH] x86/build: Fix vmlinux size check on 64-bit
Date:   Mon,  5 Oct 2020 11:15:39 -0400
Message-Id: <20201005151539.2214095-1-nivedita@alum.mit.edu>
MIME-Version: 1.0
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Commit b4e0409a36f4 ("x86: check vmlinux limits, 64-bit") added a check
that the size of the 64-bit kernel is less than KERNEL_IMAGE_SIZE.

The check uses (_end - _text), but this is not enough. The initial PMD
used in startup_64() (level2_kernel_pgt) can only map upto
KERNEL_IMAGE_SIZE from __START_KERNEL_map, not from _text.

The correct check is the same as for 32-bit, since LOAD_OFFSET is
defined appropriately for the two architectures. Just check
(_end - LOAD_OFFSET) against KERNEL_IMAGE_SIZE unconditionally.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
 arch/x86/kernel/vmlinux.lds.S | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index bf9e0adb5b7e..b38832821b98 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -454,13 +454,12 @@ SECTIONS
 	ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
 }
 
-#ifdef CONFIG_X86_32
 /*
  * The ASSERT() sink to . is intentional, for binutils 2.14 compatibility:
  */
 . = ASSERT((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),
 	   "kernel image bigger than KERNEL_IMAGE_SIZE");
-#else
+#ifdef CONFIG_X86_64
 /*
  * Per-cpu symbols which need to be offset from __per_cpu_load
  * for the boot processor.
@@ -470,18 +469,12 @@ INIT_PER_CPU(gdt_page);
 INIT_PER_CPU(fixed_percpu_data);
 INIT_PER_CPU(irq_stack_backing_store);
 
-/*
- * Build-time check on the image size:
- */
-. = ASSERT((_end - _text <= KERNEL_IMAGE_SIZE),
-	   "kernel image bigger than KERNEL_IMAGE_SIZE");
-
 #ifdef CONFIG_SMP
 . = ASSERT((fixed_percpu_data == 0),
            "fixed_percpu_data is not at start of per-cpu area");
 #endif
 
-#endif /* CONFIG_X86_32 */
+#endif /* CONFIG_X86_64 */
 
 #ifdef CONFIG_KEXEC_CORE
 #include <asm/kexec.h>
-- 
2.26.2