----- On Jul 6, 2018, at 12:02 PM, Mathieu Desnoyers [email protected] wrote:
> ----- On Jul 5, 2018, at 2:05 PM, Mathieu Desnoyers > [email protected] 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 <[email protected]> CC: Thomas Gleixner <[email protected]> Cc: Joel Fernandes <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Catalin Marinas <[email protected]> Cc: Dave Watson <[email protected]> Cc: Will Deacon <[email protected]> Cc: Andi Kleen <[email protected]> Cc: "H . Peter Anvin" <[email protected]> Cc: Chris Lameter <[email protected]> Cc: Russell King <[email protected]> Cc: Andrew Hunter <[email protected]> Cc: Michael Kerrisk <[email protected]> Cc: "Paul E . McKenney" <[email protected]> Cc: Paul Turner <[email protected]> Cc: Boqun Feng <[email protected]> Cc: Josh Triplett <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Ben Maurer <[email protected]> Cc: [email protected] CC: [email protected] Cc: Andy Lutomirski <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Linus Torvalds <[email protected]> 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
