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Not all compilers, notably GCC < 10, have support for
__attribute__((no_stack_protector)).
Fall back to a mechanism that also works there.
Tested with GCC 9.5.0 from kernel.org crosstools.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The stackprotector support in nolibc should be enabled iff it is also
enabled in the compiler.
Use the preprocessor defines added by gcc and clang if stackprotector
support is enable to automatically do so in nolibc.
This completely removes the need for any user-visible API.
To avoid inlining the lengthy preprocessor check into every user
introduce a new header compiler.h that abstracts the logic away.
As the define NOLIBC_STACKPROTECTOR is now not user-relevant anymore
prefix it with an underscore.
Suggested-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/lkml/20230520133237.GA27501@1wt.eu/
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The all-zero pattern is one of the more probable out-of-bound writes so
add a special case to not accidentally accept it.
Also it enables the reliable detection of stack protector initialization
during testing.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Most of nolibc is already using C89 comments.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This is useful when using nolibc for security-critical tools.
Using nolibc has the advantage that the code is easily auditable and
sandboxable with seccomp as no unexpected syscalls are used.
Using compiler-assistent stack protection provides another security
mechanism.
For this to work the compiler and libc have to collaborate.
This patch adds the following parts to nolibc that are required by the
compiler:
* __stack_chk_guard: random sentinel value
* __stack_chk_fail: handler for detected stack smashes
In addition an initialization function is added that randomizes the
sentinel value.
Only support for global guards is implemented.
Register guards are useful in multi-threaded context which nolibc does
not provide support for.
Link: https://lwn.net/Articles/584225/
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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