arm64: entry: Ensure branch through syscall table is bounded under speculation (6314d90e) · Commits · 戴 / test

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 <mark.rutland@arm.com> Signed-off-by:

Will Deacon <will.deacon@arm.com> Signed-off-by:

Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/assembler.h

+11 −0

Original line number	Diff line number	Diff line
		@@ -122,6 +122,17 @@
		hint #20
		.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
		*/

arch/arm64/kernel/entry.S

+2 −0

Original line number	Diff line number	Diff line
		@@ -378,6 +378,7 @@ alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
		* 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
		@@ -935,6 +936,7 @@ 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

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