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@efficios.com Cc: Peter Zijlstra peterz@infradead.org CC: Boqun Feng boqun.feng@gmail.com CC: "Paul E. McKenney" paulmck@kernel.org Cc: Shuah Khan skhan@linuxfoundation.org CC: Carlos O'Donell carlos@redhat.com CC: Florian Weimer fweimer@redhat.com CC: linux-kselftest@vger.kernel.org CC: stable@vger.kernel.org --- 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)