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Subject[PATCH AUTOSEL 4.14 50/67] arm64: fix possible spectre-v1 write in ptrace_hbp_set_event()
Date
From: Mark Rutland <mark.rutland@arm.com>

[ Upstream commit 14d6e289a89780377f8bb09de8926d3c62d763cd ]

It's possible for userspace to control idx. Sanitize idx when using it
as an array index, to inhibit the potential spectre-v1 write gadget.

Found by smatch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
arch/arm64/kernel/ptrace.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index edaf346d13d5..34d915b6974b 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -274,19 +274,22 @@ static int ptrace_hbp_set_event(unsigned int note_type,

switch (note_type) {
case NT_ARM_HW_BREAK:
- if (idx < ARM_MAX_BRP) {
- tsk->thread.debug.hbp_break[idx] = bp;
- err = 0;
- }
+ if (idx >= ARM_MAX_BRP)
+ goto out;
+ idx = array_index_nospec(idx, ARM_MAX_BRP);
+ tsk->thread.debug.hbp_break[idx] = bp;
+ err = 0;
break;
case NT_ARM_HW_WATCH:
- if (idx < ARM_MAX_WRP) {
- tsk->thread.debug.hbp_watch[idx] = bp;
- err = 0;
- }
+ if (idx >= ARM_MAX_WRP)
+ goto out;
+ idx = array_index_nospec(idx, ARM_MAX_WRP);
+ tsk->thread.debug.hbp_watch[idx] = bp;
+ err = 0;
break;
}

+out:
return err;
}

--
2.17.1
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