linux-hardening - [PATCH v2 5/5] crypto: x86/crc32c - Tweak jump table to validate objtool logic

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Message-ID: <20241010122801.1321976-12-ardb+git@google.com>
Date: Thu, 10 Oct 2024 14:28:07 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: llvm@...ts.linux.dev, keescook@...omium.org, 
	linux-hardening@...r.kernel.org, nathan@...nel.org, 
	Ard Biesheuvel <ardb@...nel.org>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Jan Beulich <jbeulich@...e.com>, 
	"Jose E. Marchesi" <jemarch@....org>, Kees Cook <kees@...nel.org>
Subject: [PATCH v2 5/5] crypto: x86/crc32c - Tweak jump table to validate
 objtool logic

From: Ard Biesheuvel <ardb@...nel.org>

Tweak the jump table so
- the address is taken far way from its use
- its offset from the start of .rodata is != 0x0
- its type is STT_OBJECT and its size is set to the size of the actual
  table
- the indirect jump is annotated with a R_X86_64_NONE relocation
  pointing to the jump table

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/crypto/crc32c-pcl-intel-asm_64.S | 39 +++++++++++---------
 1 file changed, 22 insertions(+), 17 deletions(-)

diff --git a/arch/x86/crypto/crc32c-pcl-intel-asm_64.S b/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
index 45b005935194..ba1cca66875b 100644
--- a/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
+++ b/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
@@ -93,10 +93,13 @@ SYM_FUNC_START(crc_pcl)
 #define    crc1		%r9
 #define    crc2		%r10
 
+	pushq	%rbp
 	pushq   %rbx
 	pushq   %rdi
 	pushq   %rsi
 
+	leaq	jump_table(%rip), %rbp
+
 	## Move crc_init for Linux to a different
 	mov     crc_init_arg, crc_init
 
@@ -168,9 +171,9 @@ SYM_FUNC_START(crc_pcl)
 	xor     crc2, crc2
 
 	## branch into array
-	leaq	jump_table(%rip), %bufp
-	movslq	(%bufp,%rax,4), len
-	addq	len, %bufp
+	movslq	(%rbp,%rax,4), %bufp
+	addq	%rbp, %bufp
+	.reloc	., R_X86_64_NONE, jump_table
 	JMP_NOSPEC bufp
 
 	################################################################
@@ -310,24 +313,11 @@ LABEL less_than_ %j			# less_than_j: Length should be in
 	popq    %rsi
 	popq    %rdi
 	popq    %rbx
+	popq    %rbp
         RET
 SYM_FUNC_END(crc_pcl)
 
 .section	.rodata, "a", @progbits
-        ################################################################
-        ## jump table        Table is 129 entries x 2 bytes each
-        ################################################################
-.align 4
-jump_table:
-	i=0
-.rept 129
-.altmacro
-JMPTBL_ENTRY %i
-.noaltmacro
-	i=i+1
-.endr
-
-
 	################################################################
 	## PCLMULQDQ tables
 	## Table is 128 entries x 2 words (8 bytes) each
@@ -462,3 +452,18 @@ K_table:
 	.long 0x45cddf4e, 0xe0ac139e
 	.long 0xacfa3103, 0x6c23e841
 	.long 0xa51b6135, 0x170076fa
+
+        ################################################################
+        ## jump table        Table is 129 entries x 2 bytes each
+        ################################################################
+.align 4
+jump_table:
+	i=0
+.rept 129
+.altmacro
+JMPTBL_ENTRY %i
+.noaltmacro
+	i=i+1
+.endr
+.size	jump_table, . - jump_table
+.type	jump_table, @object
-- 
2.47.0.rc0.187.ge670bccf7e-goog