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Re: [PATCH 05/12] x86: Rename __glibc_reserved2 to ssp_base in tcbhead_t
On 07/21/2018 10:20 AM, H.J. Lu wrote:
> This will be used to implement shadow stack switching by getcontext,
> makecontext, setcontext and swapcontext.
>
> * 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.
Looks good to me.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
> ---
> 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(-)
>
> diff --git a/sysdeps/i386/nptl/tcb-offsets.sym b/sysdeps/i386/nptl/tcb-offsets.sym
> index fbac241c45..2ec9e787c1 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)
OK.
> diff --git a/sysdeps/i386/nptl/tls.h b/sysdeps/i386/nptl/tls.h
> index 21e23cd809..12285d3217 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;
OK.
> } 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 387621e88c..ae8034743b 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)
OK.
>
> -- 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 f042a0250a..e88561c934 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;
OK.
> /* 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");
OK.
> # 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");
OK.
> # endif
>
> #else /* __ASSEMBLER__ */
>