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manual: Do not mention STATIC_TLS in dynamic linker hardening recommendations

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The current toolchain does not consistently generate it, and
glibc does not use it.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
This commit is contained in:
Florian Weimer 2024-07-24 12:50:17 +02:00
parent 765325951a
commit 90842d3980
1 changed files with 12 additions and 12 deletions
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24
manual/dynlink.texi
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@ -993,21 +993,21 @@ The dynamic segment should also mention @code{BIND_NOW} on the
enough).
@item
For shared objects (not main programs), if the program header has a
@code{PT_TLS} segment, the dynamic segment (as shown by @samp{readelf
-dW}) should contain the @code{STATIC_TLS} flag on the @code{FLAGS}
line.
If @code{STATIC_TLS} is missing in shared objects, ensure that the
appropriate relocations for GNU2 TLS descriptors are used (for example,
Ensure that only static TLS relocations (thread-pointer relative offset
locations) are used, for example @code{R_AARCH64_TLS_TPREL} and
@code{X86_64_TPOFF64}. As the second-best option, and only if
compatibility with non-hardened applications using @code{dlopen} is
needed, GNU2 TLS descriptor relocations can be used (for example,
@code{R_AARCH64_TLSDESC} or @code{R_X86_64_TLSDESC}).
@item
There should not be a reference to the symbols @code{__tls_get_addr},
@code{__tls_get_offset}, @code{__tls_get_addr_opt} in the dynamic symbol
table (in the @samp{readelf -sDW} output). Thread-local storage must be
accessed using the initial-exec (static) model, or using GNU2 TLS
descriptors.
There should not be references to the traditional TLS function symbols
@code{__tls_get_addr}, @code{__tls_get_offset},
@code{__tls_get_addr_opt} in the dynamic symbol table (in the
@samp{readelf -sDW} output). Supporting global dynamic TLS relocations
(such as @code{R_AARCH64_TLS_DTPMOD}, @code{R_AARCH64_TLS_DTPREL},
@code{R_X86_64_DTPMOD64}, @code{R_X86_64_DTPOFF64}) should not be used,
either.
@item
Likewise, the functions @code{dlopen}, @code{dlmopen}, @code{dlclose}