From: Will Deacon <[email protected]>
commit 6314d90e6493 upstream.
In a similar manner to array_index_mask_nospec, this patch introduces an
assembly macro (mask_nospec64) which can be used to bound a value under
speculation. This macro is then used to ensure that the indirect branch
through the syscall table is bounded under speculation, with out-of-range
addresses speculating as calls to sys_io_setup (0).
Reviewed-by: Mark Rutland <[email protected]>
Signed-off-by: Will Deacon <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
Signed-off-by: Alex Shi <[email protected]>
---
arch/arm64/include/asm/assembler.h | 11 +++++++++++
arch/arm64/kernel/entry.S | 2 ++
2 files changed, 13 insertions(+)
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index ab3a179..a109d30 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -94,6 +94,17 @@
.endm
/*
+ * Sanitise a 64-bit bounded index wrt speculation, returning zero if out
+ * of bounds.
+ */
+ .macro mask_nospec64, idx, limit, tmp
+ sub \tmp, \idx, \limit
+ bic \tmp, \tmp, \idx
+ and \idx, \idx, \tmp, asr #63
+ csdb
+ .endm
+
+/*
* NOP sequence
*/
.macro nops, num
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 48c41ff..0a27e12 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -233,6 +233,7 @@ alternative_else_nop_endif
* x7 is reserved for the system call number in 32-bit mode.
*/
wsc_nr .req w25 // number of system calls
+xsc_nr .req x25 // number of system calls (zero-extended)
wscno .req w26 // syscall number
xscno .req x26 // syscall number (zero-extended)
stbl .req x27 // syscall table pointer
@@ -754,6 +755,7 @@ el0_svc_naked: // compat entry point
b.ne __sys_trace
cmp wscno, wsc_nr // check upper syscall limit
b.hs ni_sys
+ mask_nospec64 xscno, xsc_nr, x19 // enforce bounds for syscall number
ldr x16, [stbl, xscno, lsl #3] // address in the syscall table
blr x16 // call sys_* routine
b ret_fast_syscall
--
2.7.4