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Subject[PATCH 4.4 52/75] ARM: spectre-v1: fix syscall entry
Date
From: Russell King <rmk+kernel@armlinux.org.uk>

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>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm/kernel/entry-common.S | 18 +++++++-----------
arch/arm/kernel/entry-header.S | 25 +++++++++++++++++++++++++
2 files changed, 32 insertions(+), 11 deletions(-)

--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -223,9 +223,7 @@ 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)
@@ -258,14 +256,8 @@ __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
@@ -317,6 +309,10 @@ 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
--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -373,6 +373,31 @@
#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.

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