Adapt the rseq.c/rseq.h code to follow GNU C library changes introduced by:
glibc commit 2e456ccf0c34 ("Linux: Make __rseq_size useful for feature detection (bug 31965)")
Without this fix, rseq selftests for mm_cid fail:
./run_param_test.sh
Default parameters
Running test spinlock
Running compare-twice test spinlock
Running mm_cid test spinlock
Error: cpu id getter unavailable
[ This is based on the following branch:
https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git
branch: fixes ]
Fixes: 18c2355838e7 ("selftests/rseq: Implement rseq mm_cid field support")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: Boqun Feng <boqun.feng@xxxxxxxxx>
CC: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
CC: Carlos O'Donell <carlos@xxxxxxxxxx>
CC: Florian Weimer <fweimer@xxxxxxxxxx>
CC: linux-kselftest@xxxxxxxxxxxxxxx
CC: stable@xxxxxxxxxxxxxxx
---
tools/testing/selftests/rseq/rseq.c | 110 +++++++++++++++++++---------
tools/testing/selftests/rseq/rseq.h | 10 +--
2 files changed, 77 insertions(+), 43 deletions(-)
diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 96e812bdf8a4..5b9772cdf265 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -60,12 +60,6 @@ unsigned int rseq_size = -1U;
/* Flags used during rseq registration. */
unsigned int rseq_flags;
-/*
- * rseq feature size supported by the kernel. 0 if the registration was
- * unsuccessful.
- */
-unsigned int rseq_feature_size = -1U;
-
static int rseq_ownership;
static int rseq_reg_success; /* At least one rseq registration has succeded. */
@@ -111,6 +105,43 @@ int rseq_available(void)
}
}
+/* The rseq areas need to be at least 32 bytes. */
+static
+unsigned int get_rseq_min_alloc_size(void)
+{
+ unsigned int alloc_size = rseq_size;
+
+ if (alloc_size < ORIG_RSEQ_ALLOC_SIZE)
+ alloc_size = ORIG_RSEQ_ALLOC_SIZE;
+ return alloc_size;
+}
+
+/*
+ * Return the feature size supported by the kernel.
+ *
+ * Depending on the value returned by getauxval(AT_RSEQ_FEATURE_SIZE):
+ *
+ * 0: Return ORIG_RSEQ_FEATURE_SIZE (20)
+ * > 0: Return the value from getauxval(AT_RSEQ_FEATURE_SIZE).
+ *
+ * It should never return a value below ORIG_RSEQ_FEATURE_SIZE.
+ */
+static
+unsigned int get_rseq_kernel_feature_size(void)
+{
+ unsigned long auxv_rseq_feature_size, auxv_rseq_align;
+
+ auxv_rseq_align = getauxval(AT_RSEQ_ALIGN);
+ assert(!auxv_rseq_align || auxv_rseq_align <= RSEQ_THREAD_AREA_ALLOC_SIZE);
+
+ auxv_rseq_feature_size = getauxval(AT_RSEQ_FEATURE_SIZE);
+ assert(!auxv_rseq_feature_size || auxv_rseq_feature_size <= RSEQ_THREAD_AREA_ALLOC_SIZE);
+ if (auxv_rseq_feature_size)
+ return auxv_rseq_feature_size;
+ else
+ return ORIG_RSEQ_FEATURE_SIZE;
+}
+
int rseq_register_current_thread(void)
{
int rc;
@@ -119,7 +150,7 @@ int rseq_register_current_thread(void)
/* Treat libc's ownership as a successful registration. */
return 0;
}
- rc = sys_rseq(&__rseq_abi, rseq_size, 0, RSEQ_SIG);
+ rc = sys_rseq(&__rseq_abi, get_rseq_min_alloc_size(), 0, RSEQ_SIG);
if (rc) {
if (RSEQ_READ_ONCE(rseq_reg_success)) {
/* Incoherent success/failure within process. */
@@ -140,28 +171,12 @@ int rseq_unregister_current_thread(void)
/* Treat libc's ownership as a successful unregistration. */
return 0;
}
- rc = sys_rseq(&__rseq_abi, rseq_size, RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
+ rc = sys_rseq(&__rseq_abi, get_rseq_min_alloc_size(), RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
if (rc)
return -1;
return 0;
}
-static
-unsigned int get_rseq_feature_size(void)
-{
- unsigned long auxv_rseq_feature_size, auxv_rseq_align;
-
- auxv_rseq_align = getauxval(AT_RSEQ_ALIGN);
- assert(!auxv_rseq_align || auxv_rseq_align <= RSEQ_THREAD_AREA_ALLOC_SIZE);
-
- auxv_rseq_feature_size = getauxval(AT_RSEQ_FEATURE_SIZE);
- assert(!auxv_rseq_feature_size || auxv_rseq_feature_size <= RSEQ_THREAD_AREA_ALLOC_SIZE);
- if (auxv_rseq_feature_size)
- return auxv_rseq_feature_size;
- else
- return ORIG_RSEQ_FEATURE_SIZE;
-}
-
static __attribute__((constructor))
void rseq_init(void)
{
@@ -178,28 +193,54 @@ void rseq_init(void)
}
if (libc_rseq_size_p && libc_rseq_offset_p && libc_rseq_flags_p &&
*libc_rseq_size_p != 0) {
+ unsigned int libc_rseq_size;
+
/* rseq registration owned by glibc */
rseq_offset = *libc_rseq_offset_p;
- rseq_size = *libc_rseq_size_p;
+ libc_rseq_size = *libc_rseq_size_p;
rseq_flags = *libc_rseq_flags_p;
- rseq_feature_size = get_rseq_feature_size();
- if (rseq_feature_size > rseq_size)
- rseq_feature_size = rseq_size;
+
+ /*
+ * Previous versions of glibc expose the value
+ * 32 even though the kernel only supported 20
+ * bytes initially. Therefore treat 32 as a
+ * special-case. glibc 2.40 exposes a 20 bytes
+ * __rseq_size without using getauxval(3) to
+ * query the supported size, while still allocating a 32
+ * bytes area. Also treat 20 as a special-case.
+ *
+ * Special-cases are handled by using the following
+ * value as active feature set size:
+ *
+ * rseq_size = min(32, get_rseq_kernel_feature_size())
+ */
+ switch (libc_rseq_size) {
+ case ORIG_RSEQ_FEATURE_SIZE:
+ fallthrough;
+ case ORIG_RSEQ_ALLOC_SIZE:
+ {
+ unsigned int rseq_kernel_feature_size = get_rseq_kernel_feature_size();
+
+ if (rseq_kernel_feature_size < ORIG_RSEQ_ALLOC_SIZE)
+ rseq_size = rseq_kernel_feature_size;
+ else
+ rseq_size = ORIG_RSEQ_ALLOC_SIZE;
+ break;
+ }
+ default:
+ /* Otherwise just use the __rseq_size from libc as rseq_size. */
+ rseq_size = libc_rseq_size;
+ break;
+ }
return;
}
rseq_ownership = 1;
if (!rseq_available()) {
rseq_size = 0;
- rseq_feature_size = 0;
return;
}
rseq_offset = (void *)&__rseq_abi - rseq_thread_pointer();
rseq_flags = 0;
- rseq_feature_size = get_rseq_feature_size();
- if (rseq_feature_size == ORIG_RSEQ_FEATURE_SIZE)
- rseq_size = ORIG_RSEQ_ALLOC_SIZE;
- else
- rseq_size = RSEQ_THREAD_AREA_ALLOC_SIZE;
}
static __attribute__((destructor))
@@ -209,7 +250,6 @@ void rseq_exit(void)
return;
rseq_offset = 0;
rseq_size = -1U;
- rseq_feature_size = -1U;
rseq_ownership = 0;
}
diff --git a/tools/testing/selftests/rseq/rseq.h b/tools/testing/selftests/rseq/rseq.h
index d7364ea4d201..4e217b620e0c 100644
--- a/tools/testing/selftests/rseq/rseq.h
+++ b/tools/testing/selftests/rseq/rseq.h
@@ -68,12 +68,6 @@ extern unsigned int rseq_size;
/* Flags used during rseq registration. */
extern unsigned int rseq_flags;
-/*
- * rseq feature size supported by the kernel. 0 if the registration was
- * unsuccessful.
- */
-extern unsigned int rseq_feature_size;
-
enum rseq_mo {
RSEQ_MO_RELAXED = 0,
RSEQ_MO_CONSUME = 1, /* Unused */
@@ -193,7 +187,7 @@ static inline uint32_t rseq_current_cpu(void)
static inline bool rseq_node_id_available(void)
{
- return (int) rseq_feature_size >= rseq_offsetofend(struct rseq_abi, node_id);
+ return (int) rseq_size >= rseq_offsetofend(struct rseq_abi, node_id);
}
/*
@@ -207,7 +201,7 @@ static inline uint32_t rseq_current_node_id(void)
static inline bool rseq_mm_cid_available(void)
{
- return (int) rseq_feature_size >= rseq_offsetofend(struct rseq_abi, mm_cid);
+ return (int) rseq_size >= rseq_offsetofend(struct rseq_abi, mm_cid);
}
static inline uint32_t rseq_current_mm_cid(void)
--
2.39.2
