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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 <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Will Deacon 2018-02-05 15:34:20 +00:00 committed by Catalin Marinas
parent 4d8efc2d5e
commit 6314d90e64
2 changed files with 13 additions and 0 deletions
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11
arch/arm64/include/asm/assembler.h
View File

@ -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
*/

2
arch/arm64/kernel/entry.S
View File

@ -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