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138 lines
5.1 KiB
138 lines
5.1 KiB
commit e8f521709731ce3ae8d6f1eca30135d5c0606f02
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Author: Florian Weimer <fweimer@redhat.com>
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Date: Mon Jul 8 21:14:00 2024 +0200
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Linux: Make __rseq_size useful for feature detection (bug 31965)
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The __rseq_size value is now the active area of struct rseq
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(so 20 initially), not the full struct size including padding
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at the end (32 initially).
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Update misc/tst-rseq to print some additional diagnostics.
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Reviewed-by: Michael Jeanson <mjeanson@efficios.com>
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Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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(cherry picked from commit 2e456ccf0c34a056e3ccafac4a0c7effef14d918)
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diff --git a/manual/threads.texi b/manual/threads.texi
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index e5544ff3da8733f4..25e99c9606dcad77 100644
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--- a/manual/threads.texi
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+++ b/manual/threads.texi
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@@ -1007,8 +1007,12 @@ This variable is either zero (if restartable sequence registration
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failed or has been disabled) or the size of the restartable sequence
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registration. This can be different from the size of @code{struct rseq}
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if the kernel has extended the size of the registration. If
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-registration is successful, @code{__rseq_size} is at least 32 (the
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-initial size of @code{struct rseq}).
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+registration is successful, @code{__rseq_size} is at least 20 (the
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+initially active size of @code{struct rseq}).
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+
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+Previous versions of @theglibc{} set this to 32 even if the kernel only
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+supported the initial area of 20 bytes because the value included unused
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+padding at the end of the restartable sequence area.
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@end deftypevar
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@deftypevar {unsigned int} __rseq_flags
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diff --git a/sysdeps/nptl/dl-tls_init_tp.c b/sysdeps/nptl/dl-tls_init_tp.c
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index 7eb35fb13384f6ac..7803e19fd16ad803 100644
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--- a/sysdeps/nptl/dl-tls_init_tp.c
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+++ b/sysdeps/nptl/dl-tls_init_tp.c
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@@ -46,10 +46,6 @@ rtld_mutex_dummy (pthread_mutex_t *lock)
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const unsigned int __rseq_flags;
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-/* The variables are in .data.relro but are not yet write-protected. */
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-extern unsigned int _rseq_size attribute_hidden;
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-extern ptrdiff_t _rseq_offset attribute_hidden;
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-
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void
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__tls_pre_init_tp (void)
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{
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@@ -106,9 +102,7 @@ __tls_init_tp (void)
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bool do_rseq = true;
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do_rseq = TUNABLE_GET (rseq, int, NULL);
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if (rseq_register_current_thread (pd, do_rseq))
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- {
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- _rseq_size = sizeof (pd->rseq_area);
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- }
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+ _rseq_size = RSEQ_AREA_SIZE_INITIAL_USED;
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#ifdef RSEQ_SIG
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/* This should be a compile-time constant, but the current
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diff --git a/sysdeps/unix/sysv/linux/rseq-internal.h b/sysdeps/unix/sysv/linux/rseq-internal.h
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index 48eebc1e168fad1e..7ea935b4adab8c20 100644
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--- a/sysdeps/unix/sysv/linux/rseq-internal.h
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+++ b/sysdeps/unix/sysv/linux/rseq-internal.h
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@@ -25,15 +25,34 @@
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#include <stdio.h>
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#include <sys/rseq.h>
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+/* 32 is the initially required value for the area size. The
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+ actually used rseq size may be less (20 bytes initially). */
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+#define RSEQ_AREA_SIZE_INITIAL 32
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+#define RSEQ_AREA_SIZE_INITIAL_USED 20
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+
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+/* The variables are in .data.relro but are not yet write-protected. */
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+extern unsigned int _rseq_size attribute_hidden;
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+extern ptrdiff_t _rseq_offset attribute_hidden;
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+
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#ifdef RSEQ_SIG
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static inline bool
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rseq_register_current_thread (struct pthread *self, bool do_rseq)
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{
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if (do_rseq)
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{
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+ unsigned int size;
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+#if IS_IN (rtld)
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+ /* Use the hidden symbol in ld.so. */
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+ size = _rseq_size;
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+#else
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+ size = __rseq_size;
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+#endif
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+ if (size < RSEQ_AREA_SIZE_INITIAL)
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+ /* The initial implementation used only 20 bytes out of 32,
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+ but still expected size 32. */
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+ size = RSEQ_AREA_SIZE_INITIAL;
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int ret = INTERNAL_SYSCALL_CALL (rseq, &self->rseq_area,
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- sizeof (self->rseq_area),
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- 0, RSEQ_SIG);
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+ size, 0, RSEQ_SIG);
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if (!INTERNAL_SYSCALL_ERROR_P (ret))
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return true;
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}
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diff --git a/sysdeps/unix/sysv/linux/tst-rseq.c b/sysdeps/unix/sysv/linux/tst-rseq.c
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index 2c90409ba02182e7..08a95331306b2a12 100644
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--- a/sysdeps/unix/sysv/linux/tst-rseq.c
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+++ b/sysdeps/unix/sysv/linux/tst-rseq.c
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@@ -29,6 +29,7 @@
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# include <stdlib.h>
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# include <string.h>
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# include <syscall.h>
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+# include <sys/auxv.h>
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# include <thread_pointer.h>
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# include <tls.h>
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# include "tst-rseq.h"
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@@ -42,7 +43,8 @@ do_rseq_main_test (void)
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TEST_COMPARE (__rseq_flags, 0);
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TEST_VERIFY ((char *) __thread_pointer () + __rseq_offset
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== (char *) &pd->rseq_area);
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- TEST_COMPARE (__rseq_size, sizeof (pd->rseq_area));
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+ /* The current implementation only supports the initial size. */
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+ TEST_COMPARE (__rseq_size, 20);
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}
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static void
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@@ -52,6 +54,12 @@ do_rseq_test (void)
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{
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FAIL_UNSUPPORTED ("kernel does not support rseq, skipping test");
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}
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+ printf ("info: __rseq_size: %u\n", __rseq_size);
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+ printf ("info: __rseq_offset: %td\n", __rseq_offset);
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+ printf ("info: __rseq_flags: %u\n", __rseq_flags);
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+ printf ("info: getauxval (AT_RSEQ_FEATURE_SIZE): %ld\n",
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+ getauxval (AT_RSEQ_FEATURE_SIZE));
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+ printf ("info: getauxval (AT_RSEQ_ALIGN): %ld\n", getauxval (AT_RSEQ_ALIGN));
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do_rseq_main_test ();
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}
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#else /* RSEQ_SIG */
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