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
