From 9aa3113a42d94d7bbf9bb4d50ef0d23b95e66123 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Wed, 25 Jul 2018 04:39:26 -0700 Subject: x86: Rename __glibc_reserved2 to ssp_base in tcbhead_t This will be used to record the current shadow stack base for shadow stack switching by getcontext, makecontext, setcontext and swapcontext. If the target shadow stack base is the same as the current shadow stack base, we unwind the shadow stack. Otherwise it is a stack switch and we look for a restore token to restore the target shadow stack. * sysdeps/i386/nptl/tcb-offsets.sym (SSP_BASE_OFFSET): New. * sysdeps/i386/nptl/tls.h (tcbhead_t): Replace __glibc_reserved2 with ssp_base. * sysdeps/x86_64/nptl/tcb-offsets.sym (SSP_BASE_OFFSET): New. * sysdeps/x86_64/nptl/tls.h (tcbhead_t): Replace __glibc_reserved2 with ssp_base. --- sysdeps/i386/nptl/tcb-offsets.sym | 1 + sysdeps/i386/nptl/tls.h | 3 ++- sysdeps/x86_64/nptl/tcb-offsets.sym | 1 + sysdeps/x86_64/nptl/tls.h | 10 +++++++++- 4 files changed, 13 insertions(+), 2 deletions(-) (limited to 'sysdeps') diff --git a/sysdeps/i386/nptl/tcb-offsets.sym b/sysdeps/i386/nptl/tcb-offsets.sym index fbac241..2ec9e78 100644 --- a/sysdeps/i386/nptl/tcb-offsets.sym +++ b/sysdeps/i386/nptl/tcb-offsets.sym @@ -13,3 +13,4 @@ CLEANUP_PREV offsetof (struct _pthread_cleanup_buffer, __prev) MUTEX_FUTEX offsetof (pthread_mutex_t, __data.__lock) POINTER_GUARD offsetof (tcbhead_t, pointer_guard) FEATURE_1_OFFSET offsetof (tcbhead_t, feature_1) +SSP_BASE_OFFSET offsetof (tcbhead_t, ssp_base) diff --git a/sysdeps/i386/nptl/tls.h b/sysdeps/i386/nptl/tls.h index 21e23cd..12285d3 100644 --- a/sysdeps/i386/nptl/tls.h +++ b/sysdeps/i386/nptl/tls.h @@ -49,7 +49,8 @@ typedef struct void *__private_tm[3]; /* GCC split stack support. */ void *__private_ss; - void *__glibc_reserved2; + /* The lowest address of shadow stack, */ + unsigned long ssp_base; } tcbhead_t; /* morestack.S in libgcc uses offset 0x30 to access __private_ss, */ diff --git a/sysdeps/x86_64/nptl/tcb-offsets.sym b/sysdeps/x86_64/nptl/tcb-offsets.sym index 387621e..ae80347 100644 --- a/sysdeps/x86_64/nptl/tcb-offsets.sym +++ b/sysdeps/x86_64/nptl/tcb-offsets.sym @@ -13,6 +13,7 @@ MULTIPLE_THREADS_OFFSET offsetof (tcbhead_t, multiple_threads) POINTER_GUARD offsetof (tcbhead_t, pointer_guard) VGETCPU_CACHE_OFFSET offsetof (tcbhead_t, vgetcpu_cache) FEATURE_1_OFFSET offsetof (tcbhead_t, feature_1) +SSP_BASE_OFFSET offsetof (tcbhead_t, ssp_base) -- Not strictly offsets, but these values are also used in the TCB. TCB_CANCELSTATE_BITMASK CANCELSTATE_BITMASK diff --git a/sysdeps/x86_64/nptl/tls.h b/sysdeps/x86_64/nptl/tls.h index f042a02..e88561c 100644 --- a/sysdeps/x86_64/nptl/tls.h +++ b/sysdeps/x86_64/nptl/tls.h @@ -60,7 +60,8 @@ typedef struct void *__private_tm[4]; /* GCC split stack support. */ void *__private_ss; - long int __glibc_reserved2; + /* The lowest address of shadow stack, */ + unsigned long long int ssp_base; /* Must be kept even if it is no longer used by glibc since programs, like AddressSanitizer, depend on the size of tcbhead_t. */ __128bits __glibc_unused2[8][4] __attribute__ ((aligned (32))); @@ -72,10 +73,17 @@ typedef struct /* morestack.S in libgcc uses offset 0x40 to access __private_ss, */ _Static_assert (offsetof (tcbhead_t, __private_ss) == 0x40, "offset of __private_ss != 0x40"); +/* NB: ssp_base used to be "long int __glibc_reserved2", which was + changed from 32 bits to 64 bits. Make sure that the offset of the + next field, __glibc_unused2, is unchanged. */ +_Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x60, + "offset of __glibc_unused2 != 0x60"); # else /* morestack.S in libgcc uses offset 0x70 to access __private_ss, */ _Static_assert (offsetof (tcbhead_t, __private_ss) == 0x70, "offset of __private_ss != 0x70"); +_Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80, + "offset of __glibc_unused2 != 0x80"); # endif #else /* __ASSEMBLER__ */ -- cgit v1.1