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Subject[tip: x86/mm] prctl: Hook L1D flushing in via prctl
The following commit has been merged into the x86/mm branch of tip:

Commit-ID: edf7ce0b231cb6cdc170125588cf71c70358fc74
Gitweb: https://git.kernel.org/tip/edf7ce0b231cb6cdc170125588cf71c70358fc74
Author: Balbir Singh <sblbir@amazon.com>
AuthorDate: Sat, 16 May 2020 20:34:29 +10:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Fri, 22 May 2020 10:36:48 +02:00

prctl: Hook L1D flushing in via prctl

Use the existing PR_GET/SET_SPECULATION_CTRL API to expose the L1D
flush capability. For L1D flushing PR_SPEC_FORCE_DISABLE and
PR_SPEC_DISABLE_NOEXEC are not supported.

There is also no seccomp integration for the feature.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Balbir Singh <sblbir@amazon.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200516103430.26527-3-sblbir@amazon.com

---
arch/x86/kernel/cpu/bugs.c | 28 ++++++++++++++++++++++++++++
include/uapi/linux/prctl.h | 1 +
2 files changed, 29 insertions(+)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index ed54b3b..3eb9139 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1121,6 +1121,19 @@ static void task_update_spec_tif(struct task_struct *tsk)
speculation_ctrl_update_current();
}

+static int l1d_flush_out_prctl_set(struct task_struct *task, unsigned long ctrl)
+{
+ switch (ctrl) {
+ case PR_SPEC_ENABLE:
+ return enable_l1d_flush_for_task(task);
+ case PR_SPEC_DISABLE:
+ return disable_l1d_flush_for_task(task);
+ default:
+ return -ERANGE;
+ }
+ return 0;
+}
+
static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
{
if (ssb_mode != SPEC_STORE_BYPASS_PRCTL &&
@@ -1206,6 +1219,8 @@ int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
return ssb_prctl_set(task, ctrl);
case PR_SPEC_INDIRECT_BRANCH:
return ib_prctl_set(task, ctrl);
+ case PR_SPEC_L1D_FLUSH_OUT:
+ return l1d_flush_out_prctl_set(task, ctrl);
default:
return -ENODEV;
}
@@ -1221,6 +1236,17 @@ void arch_seccomp_spec_mitigate(struct task_struct *task)
}
#endif

+static int l1d_flush_out_prctl_get(struct task_struct *task)
+{
+ int ret;
+
+ ret = test_ti_thread_flag(&task->thread_info, TIF_SPEC_L1D_FLUSH);
+ if (ret)
+ return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
+ else
+ return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
+}
+
static int ssb_prctl_get(struct task_struct *task)
{
switch (ssb_mode) {
@@ -1272,6 +1298,8 @@ int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
return ssb_prctl_get(task);
case PR_SPEC_INDIRECT_BRANCH:
return ib_prctl_get(task);
+ case PR_SPEC_L1D_FLUSH_OUT:
+ return l1d_flush_out_prctl_get(task);
default:
return -ENODEV;
}
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 07b4f81..1e86486 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -213,6 +213,7 @@ struct prctl_mm_map {
/* Speculation control variants */
# define PR_SPEC_STORE_BYPASS 0
# define PR_SPEC_INDIRECT_BRANCH 1
+# define PR_SPEC_L1D_FLUSH_OUT 2
/* Return and control values for PR_SET/GET_SPECULATION_CTRL */
# define PR_SPEC_NOT_AFFECTED 0
# define PR_SPEC_PRCTL (1UL << 0)
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