linux-kernel - [PATCH v7 02/12] x86: Use symbol name in jump table for PIE support

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Message-Id: <20190520231948.49693-3-thgarnie@chromium.org>
Date:   Mon, 20 May 2019 16:19:27 -0700
From:   Thomas Garnier <thgarnie@...omium.org>
To:     kernel-hardening@...ts.openwall.com
Cc:     kristen@...ux.intel.com, Thomas Garnier <thgarnie@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Nadav Amit <namit@...are.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v7 02/12] x86: Use symbol name in jump table for PIE support

From: Thomas Garnier <thgarnie@...gle.com>

Replace the %c constraint with %P. The %c is incompatible with PIE
because it implies an immediate value whereas %P reference a symbol.
Change the _ASM_PTR reference to .long for expected relocation size and
add a long padding to ensure entry alignment.

Position Independent Executable (PIE) support will allow to extend the
KASLR randomization range below 0xffffffff80000000.

Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
 arch/x86/include/asm/jump_label.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index 65191ce8e1cf..e47fad8ee632 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -25,9 +25,9 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
 		".pushsection __jump_table,  \"aw\" \n\t"
 		_ASM_ALIGN "\n\t"
 		".long 1b - ., %l[l_yes] - . \n\t"
-		_ASM_PTR "%c0 + %c1 - .\n\t"
+		_ASM_PTR "%P0 - .\n\t"
 		".popsection \n\t"
-		: :  "i" (key), "i" (branch) : : l_yes);
+		: :  "X" (&((char *)key)[branch]) : : l_yes);
 
 	return false;
 l_yes:
@@ -42,9 +42,9 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
 		".pushsection __jump_table,  \"aw\" \n\t"
 		_ASM_ALIGN "\n\t"
 		".long 1b - ., %l[l_yes] - . \n\t"
-		_ASM_PTR "%c0 + %c1 - .\n\t"
+		_ASM_PTR "%P0 - .\n\t"
 		".popsection \n\t"
-		: :  "i" (key), "i" (branch) : : l_yes);
+		: : "X" (&((char *)key)[branch]) : : l_yes);
 
 	return false;
 l_yes:
-- 
2.21.0.1020.gf2820cf01a-goog