arm64: entry: Ensure branch through syscall table is bounded under speculation
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Web: https://git.kernel.org/torvalds/c/6314d90e64936c584f300a52ef173603fb2461b5 Commit: 6314d90e64936c584f300a52ef173603fb2461b5 Parent: 4d8efc2d5ee4c9ccfeb29ee8afd47a8660d0c0ce Refname: refs/heads/master Author: Will Deacon <[email protected]> AuthorDate: Mon Feb 5 15:34:20 2018 +0000 Committer: Catalin Marinas <[email protected]> CommitDate: Tue Feb 6 22:53:35 2018 +0000 arm64: entry: Ensure branch through syscall table is bounded under speculation 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]> --- 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 1f44b4255a28..1241fb211293 100644 --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -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 */ diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 17c15f741780..4dd1b5a46642 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -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 -- To unsubscribe from this list: send the line "unsubscribe git-commits-head" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html