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Date:   Fri, 23 Apr 2021 13:51:59 -0700
Message-Id: <20210423205159.830854-1-morbo@google.com>
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Subject: [PATCH] arm64/vdso: Discard .note.gnu.property sections in vDSO
From:   Bill Wendling <morbo@google.com>
To:     Kees Cook <keescook@google.com>, Ard Biesheuvel <ardb@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org
Cc:     Bill Wendling <morbo@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

The arm64 assembler in binutils 2.32 and above generates a program
property note in a note section, .note.gnu.property, to encode used x86
ISAs and features. But the kernel linker script only contains a single
NOTE segment:

  PHDRS
  {
    text    PT_LOAD    FLAGS(5) FILEHDR PHDRS; /* PF_R|PF_X */
    dynamic PT_DYNAMIC FLAGS(4);               /* PF_R */
    note    PT_NOTE    FLAGS(4);               /* PF_R */
  }

The NOTE segment generated by the vDSO linker script is aligned to 4 bytes.
But the .note.gnu.property section must be aligned to 8 bytes on arm64.

  $ readelf -n vdso64.so

  Displaying notes found in: .note
    Owner                Data size      Description
    Linux                0x00000004     Unknown note type: (0x00000000)
     description data: 06 00 00 00
  readelf: Warning: note with invalid namesz and/or descsz found at offset 0x20
  readelf: Warning:  type: 0x78, namesize: 0x00000100, descsize: 0x756e694c, alignment: 8

Since the note.gnu.property section in the vDSO is not checked by the
dynamic linker, discard the .note.gnu.property sections in the vDSO.

Similar to commit 4caffe6a28d31 ("x86/vdso: Discard .note.gnu.property
sections in vDSO"), but for arm64.

Signed-off-by: Bill Wendling <morbo@google.com>
---
 arch/arm64/kernel/vdso/vdso.lds.S | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/vdso/vdso.lds.S b/arch/arm64/kernel/vdso/vdso.lds.S
index 61dbb4c838ef..a5e61e09ea92 100644
--- a/arch/arm64/kernel/vdso/vdso.lds.S
+++ b/arch/arm64/kernel/vdso/vdso.lds.S
@@ -31,6 +31,13 @@ SECTIONS
 	.gnu.version_d	: { *(.gnu.version_d) }
 	.gnu.version_r	: { *(.gnu.version_r) }
 
+	/*
+	 * Discard .note.gnu.property sections which are unused and have
+	 * different alignment requirement from vDSO note sections.
+	 */
+	/DISCARD/	: {
+		*(.note.GNU-stack .note.gnu.property)
+	}
 	.note		: { *(.note.*) }		:text	:note
 
 	. = ALIGN(16);
@@ -48,7 +55,6 @@ SECTIONS
 	PROVIDE(end = .);
 
 	/DISCARD/	: {
-		*(.note.GNU-stack)
 		*(.data .data.* .gnu.linkonce.d.* .sdata*)
 		*(.bss .sbss .dynbss .dynsbss)
 		*(.eh_frame .eh_frame_hdr)
-- 
2.31.1.498.g6c1eba8ee3d-goog