git: 4b136ef259ce - main - amd64: Set GS.base before calling init_secondary() on APs
Mark Johnston
markj at FreeBSD.org
Thu Jul 29 14:49:14 UTC 2021
The branch main has been updated by markj:
URL: https://cgit.FreeBSD.org/src/commit/?id=4b136ef259cefedc9b6404afc09138aeb8acbd91
commit 4b136ef259cefedc9b6404afc09138aeb8acbd91
Author: Mark Johnston <markj at FreeBSD.org>
AuthorDate: 2021-07-29 14:22:37 +0000
Commit: Mark Johnston <markj at FreeBSD.org>
CommitDate: 2021-07-29 14:22:37 +0000
amd64: Set GS.base before calling init_secondary() on APs
KMSAN instrumentation requires thread-local storage to track
initialization state for function parameters and return values. This
buffer is accessed as part of each function prologue. It is provided by
the KMSAN runtime, which looks up a pointer in the current thread's
structure.
When KMSAN is configured, init_secondary() is instrumented, but this
means that GS.base must be initialized first, otherwise the runtime
cannot safely access curthread. Work around this by loading GS.base
before calling init_secondary(), so that the runtime can at least check
curthread == NULL and return a pointer to some dummy storage. Note that
init_secondary() still must reload GS.base after calling lgdt(), which
loads a selector into %gs, which in turn clears the base register.
Reviewed by: kib
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D31336
---
sys/amd64/amd64/mp_machdep.c | 8 ++++----
sys/amd64/amd64/mpboot.S | 17 +++++++++++++++++
2 files changed, 21 insertions(+), 4 deletions(-)
diff --git a/sys/amd64/amd64/mp_machdep.c b/sys/amd64/amd64/mp_machdep.c
index 86a5d78c8a8e..343589ae4c6a 100644
--- a/sys/amd64/amd64/mp_machdep.c
+++ b/sys/amd64/amd64/mp_machdep.c
@@ -103,6 +103,7 @@ static char *doublefault_stack;
static char *mce_stack;
static char *nmi_stack;
static char *dbg_stack;
+void *bootpcpu;
extern u_int mptramp_la57;
extern u_int mptramp_nx;
@@ -197,10 +198,8 @@ init_secondary(void)
/* Update microcode before doing anything else. */
ucode_load_ap(cpu);
- /* Get per-cpu data and save */
- pc = &__pcpu[cpu];
-
- /* prime data page for it to use */
+ /* Initialize the PCPU area. */
+ pc = bootpcpu;
pcpu_init(pc, cpu, sizeof(struct pcpu));
dpcpu_init(dpcpu, cpu);
pc->pc_apic_id = cpu_apic_ids[cpu];
@@ -431,6 +430,7 @@ start_all_aps(void)
dpcpu = (void *)kmem_malloc_domainset(DOMAINSET_PREF(domain),
DPCPU_SIZE, M_WAITOK | M_ZERO);
+ bootpcpu = &__pcpu[cpu];
bootSTK = (char *)bootstacks[cpu] +
kstack_pages * PAGE_SIZE - 8;
bootAP = cpu;
diff --git a/sys/amd64/amd64/mpboot.S b/sys/amd64/amd64/mpboot.S
index b6c599a2aff3..1b5657d3bef8 100644
--- a/sys/amd64/amd64/mpboot.S
+++ b/sys/amd64/amd64/mpboot.S
@@ -260,4 +260,21 @@ bootMP_size:
.p2align 4,0
entry_64:
movq bootSTK, %rsp
+
+ /*
+ * Initialize the segment register used for the PCPU area. The PCPU
+ * area will be initialized by init_secondary(), but it should be
+ * accessible before that to support sanitizer instrumentation which
+ * accesses per-CPU variables.
+ *
+ * Note that GS.base is loaded again in init_secondary(). This is not
+ * redundant: lgdt() loads a selector into %gs and this has the side
+ * effect of clearing GS.base.
+ */
+ movl $MSR_GSBASE, %ecx
+ movq bootpcpu, %rax
+ movq %rax, %rdx
+ shrq $32, %rdx
+ wrmsr
+
jmp init_secondary
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