From: Ard Biesheuvel <[email protected]>
Tweak the asm crc32c asm code so that the jump table is more difficult
to decipher for objtool:
- load the address in the prologue
- move the jump table to the middle of .rodata, so that the section
offset and the symbol offset differ
- emit an entry following the jump table that is unrelated
- add unconditional ENDBRs so we can test --ibt regardless of the kernel
config
Test code only. Not intended for merging.
---
arch/x86/crypto/crc32c-pcl-intel-asm_64.S | 50 +++++++++++---------
1 file changed, 28 insertions(+), 22 deletions(-)
diff --git a/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
b/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
index 7292090e76dd..cbedf5820e30 100644
--- a/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
+++ b/arch/x86/crypto/crc32c-pcl-intel-asm_64.S
@@ -93,10 +93,14 @@ SYM_FUNC_START(crc_pcl)
#define crc1 %r9
#define crc2 %r10
+ endbr64
+ 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 +172,8 @@ 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
@@ -197,7 +200,7 @@ SYM_FUNC_START(crc_pcl)
.altmacro
LABEL crc_ %i
.noaltmacro
- ENDBR
+ endbr64
crc32q -i*8(block_0), crc_init
crc32q -i*8(block_1), crc1
crc32q -i*8(block_2), crc2
@@ -207,7 +210,7 @@ LABEL crc_ %i
.altmacro
LABEL crc_ %i
.noaltmacro
- ENDBR
+ endbr64
crc32q -i*8(block_0), crc_init
crc32q -i*8(block_1), crc1
# SKIP crc32 -i*8(block_2), crc2 ; Don't do this one yet
@@ -241,7 +244,7 @@ LABEL crc_ %i
################################################################
LABEL crc_ 0
- ENDBR
+ endbr64
mov tmp, len
cmp $128*24, tmp
jae .Lfull_block
@@ -311,26 +314,11 @@ 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
-
-.size jump_table, . - jump_table
-.type jump_table, @object
-
################################################################
## PCLMULQDQ tables
## Table is 128 entries x 2 words (8 bytes) each
@@ -465,3 +453,21 @@ 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
+
+ .long crc_pcl - .
--
2.47.0.rc1.288.g06298d1525-goog
