----- On Jul 6, 2018, at 12:02 PM, Mathieu Desnoyers mathieu.desnoyers@xxxxxxxxxxxx wrote:
> ----- On Jul 5, 2018, at 2:05 PM, Mathieu Desnoyers
> mathieu.desnoyers@xxxxxxxxxxxx wrote:
>
[...]
> The 0-day bot noticed that __get_user() is unimplemented for 64-bit
> values on arm32 (although get_user() is implemented).
>
> The following diff fixes this discrepancy, and allows this rseq patch
> to build on arm32:
>
For -rc, I would favor the following simpler approach. Or I could even
just use get_user() instead. Thoughts ?
rseq: implement work-around for missing 8-byte __get_user on arm
Now that rseq uses __u64 for its pointer fields, 32-bit architectures
need to read this 64-bit value from user-space.
__get_user is used to read this value, given that its access check has
already been performed with access_ok() on rseq registration.
arm does not implement 8-byte __get_user. Work-around this limitation
by using get_user() on ARM instead, with its redundant access check.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Joel Fernandes <joelaf@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Dave Watson <davejwatson@xxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: "H . Peter Anvin" <hpa@xxxxxxxxx>
Cc: Chris Lameter <cl@xxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
Cc: Andrew Hunter <ahh@xxxxxxxxxx>
Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
Cc: "Paul E . McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Paul Turner <pjt@xxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ben Maurer <bmaurer@xxxxxx>
Cc: linux-api@xxxxxxxxxxxxxxx
CC: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
diff --git a/kernel/rseq.c b/kernel/rseq.c
index 3081e67..0e67625 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -18,6 +18,16 @@
#define CREATE_TRACE_POINTS
#include <trace/events/rseq.h>
+/*
+ * ARM does not implement 8 bytes __get_user. Use get_user on that
+ * architecture instead.
+ */
+#ifdef CONFIG_ARM
+#define __rseq_get_user get_user
+#else
+#define __rseq_get_user __get_user
+#endif
+
#define RSEQ_CS_PREEMPT_MIGRATE_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE | \
RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT)
@@ -120,7 +130,7 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rs
u32 sig;
int ret;
- ret = __get_user(ptr, &t->rseq->rseq_cs.ptr64);
+ ret = __rseq_get_user(ptr, &t->rseq->rseq_cs.ptr64);
if (ret)
return ret;
if (!ptr) {
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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