ARM: spectre-v1: fix syscall entry

Commit 10573ae547c85b2c61417ff1a106cffbfceada35 upstream.

Prevent speculation at the syscall table decoding by clamping the index
used to zero on invalid system call numbers, and using the csdb
speculative barrier.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Boot-tested-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: David A. Long <dave.long@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 99c9082..54c1050 100644 (file)
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -241,9 +241,7 @@ local_restart:
        tst     r10, #_TIF_SYSCALL_WORK         @ are we tracing syscalls?
        bne     __sys_trace
 
-       cmp     scno, #NR_syscalls              @ check upper syscall limit
-       badr    lr, ret_fast_syscall            @ return address
-       ldrcc   pc, [tbl, scno, lsl #2]         @ call sys_* routine
+       invoke_syscall tbl, scno, r10, ret_fast_syscall
 
        add     r1, sp, #S_OFF
 2:     cmp     scno, #(__ARM_NR_BASE - __NR_SYSCALL_BASE)
@@ -277,14 +275,8 @@ __sys_trace:
        mov     r1, scno
        add     r0, sp, #S_OFF
        bl      syscall_trace_enter
-
-       badr    lr, __sys_trace_return          @ return address
-       mov     scno, r0                        @ syscall number (possibly new)
-       add     r1, sp, #S_R0 + S_OFF           @ pointer to regs
-       cmp     scno, #NR_syscalls              @ check upper syscall limit
-       ldmccia r1, {r0 - r6}                   @ have to reload r0 - r6
-       stmccia sp, {r4, r5}                    @ and update the stack args
-       ldrcc   pc, [tbl, scno, lsl #2]         @ call sys_* routine
+       mov     scno, r0
+       invoke_syscall tbl, scno, r10, __sys_trace_return, reload=1
        cmp     scno, #-1                       @ skip the syscall?
        bne     2b
        add     sp, sp, #S_OFF                  @ restore stack
@@ -362,6 +354,10 @@ sys_syscall:
                bic     scno, r0, #__NR_OABI_SYSCALL_BASE
                cmp     scno, #__NR_syscall - __NR_SYSCALL_BASE
                cmpne   scno, #NR_syscalls      @ check range
+#ifdef CONFIG_CPU_SPECTRE
+               movhs   scno, #0
+               csdb
+#endif
                stmloia sp, {r5, r6}            @ shuffle args
                movlo   r0, r1
                movlo   r1, r2

diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
index 0f07579..7734248 100644 (file)
--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -378,6 +378,31 @@
 #endif
        .endm
 
+       .macro  invoke_syscall, table, nr, tmp, ret, reload=0
+#ifdef CONFIG_CPU_SPECTRE
+       mov     \tmp, \nr
+       cmp     \tmp, #NR_syscalls              @ check upper syscall limit
+       movcs   \tmp, #0
+       csdb
+       badr    lr, \ret                        @ return address
+       .if     \reload
+       add     r1, sp, #S_R0 + S_OFF           @ pointer to regs
+       ldmccia r1, {r0 - r6}                   @ reload r0-r6
+       stmccia sp, {r4, r5}                    @ update stack arguments
+       .endif
+       ldrcc   pc, [\table, \tmp, lsl #2]      @ call sys_* routine
+#else
+       cmp     \nr, #NR_syscalls               @ check upper syscall limit
+       badr    lr, \ret                        @ return address
+       .if     \reload
+       add     r1, sp, #S_R0 + S_OFF           @ pointer to regs
+       ldmccia r1, {r0 - r6}                   @ reload r0-r6
+       stmccia sp, {r4, r5}                    @ update stack arguments
+       .endif
+       ldrcc   pc, [\table, \nr, lsl #2]       @ call sys_* routine
+#endif
+       .endm
+
 /*
  * These are the registers used in the syscall handler, and allow us to
  * have in theory up to 7 arguments to a function - r0 to r6.