----- On Feb 26, 2021, at 8:51 AM, Piotr Figiel figiel@xxxxxxxxxx wrote: > For userspace checkpoint and restore (C/R) a way of getting process state > containing RSEQ configuration is needed. > > There are two ways this information is going to be used: > - to re-enable RSEQ for threads which had it enabled before C/R > - to detect if a thread was in a critical section during C/R > > Since C/R preserves TLS memory and addresses RSEQ ABI will be restored > using the address registered before C/R. > > Detection whether the thread is in a critical section during C/R is needed > to enforce behavior of RSEQ abort during C/R. Attaching with ptrace() > before registers are dumped itself doesn't cause RSEQ abort. > Restoring the instruction pointer within the critical section is > problematic because rseq_cs may get cleared before the control is passed > to the migrated application code leading to RSEQ invariants not being > preserved. C/R code will use RSEQ ABI address to find the abort handler > to which the instruction pointer needs to be set. > > To achieve above goals expose the RSEQ ABI address and the signature value > with the new ptrace request PTRACE_GET_RSEQ_CONFIGURATION. > > This new ptrace request can also be used by debuggers so they are aware > of stops within restartable sequences in progress. > > Signed-off-by: Piotr Figiel <figiel@xxxxxxxxxx> > Reviewed-by: Michal Miroslaw <emmir@xxxxxxxxxx> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> Thanks! Mathieu > > --- > v2: > Applied review comments: > - changed return value from the ptrace request to the size of the > configuration structure > - expanded configuration structure with the flags field and > the rseq abi structure size > > v1: > https://lore.kernel.org/lkml/20210222100443.4155938-1-figiel@xxxxxxxxxx/ > > --- > include/uapi/linux/ptrace.h | 10 ++++++++++ > kernel/ptrace.c | 25 +++++++++++++++++++++++++ > 2 files changed, 35 insertions(+) > > diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h > index 83ee45fa634b..3747bf816f9a 100644 > --- a/include/uapi/linux/ptrace.h > +++ b/include/uapi/linux/ptrace.h > @@ -102,6 +102,16 @@ struct ptrace_syscall_info { > }; > }; > > +#define PTRACE_GET_RSEQ_CONFIGURATION 0x420f > + > +struct ptrace_rseq_configuration { > + __u64 rseq_abi_pointer; > + __u32 rseq_abi_size; > + __u32 signature; > + __u32 flags; > + __u32 pad; > +}; > + > /* > * These values are stored in task->ptrace_message > * by tracehook_report_syscall_* to describe the current syscall-stop. > diff --git a/kernel/ptrace.c b/kernel/ptrace.c > index 61db50f7ca86..76f09456ec4b 100644 > --- a/kernel/ptrace.c > +++ b/kernel/ptrace.c > @@ -31,6 +31,7 @@ > #include <linux/cn_proc.h> > #include <linux/compat.h> > #include <linux/sched/signal.h> > +#include <linux/minmax.h> > > #include <asm/syscall.h> /* for syscall_get_* */ > > @@ -779,6 +780,24 @@ static int ptrace_peek_siginfo(struct task_struct *child, > return ret; > } > > +#ifdef CONFIG_RSEQ > +static long ptrace_get_rseq_configuration(struct task_struct *task, > + unsigned long size, void __user *data) > +{ > + struct ptrace_rseq_configuration conf = { > + .rseq_abi_pointer = (u64)(uintptr_t)task->rseq, > + .rseq_abi_size = sizeof(*task->rseq), > + .signature = task->rseq_sig, > + .flags = 0, > + }; > + > + size = min_t(unsigned long, size, sizeof(conf)); > + if (copy_to_user(data, &conf, size)) > + return -EFAULT; > + return sizeof(conf); > +} > +#endif > + > #ifdef PTRACE_SINGLESTEP > #define is_singlestep(request) ((request) == PTRACE_SINGLESTEP) > #else > @@ -1222,6 +1241,12 @@ int ptrace_request(struct task_struct *child, long > request, > ret = seccomp_get_metadata(child, addr, datavp); > break; > > +#ifdef CONFIG_RSEQ > + case PTRACE_GET_RSEQ_CONFIGURATION: > + ret = ptrace_get_rseq_configuration(child, addr, datavp); > + break; > +#endif > + > default: > break; > } > -- > 2.30.1.766.gb4fecdf3b7-goog -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
