SEC, PEI_CORE and PEIM type modules generally execute in place from
memory that is not writable. This means that it is not generally
possible to use an entrypoint implementation that stores a dynamically
generated stack cookie into a global variable. For PEIMs in particular,
there may be other options, such as a DEPEX on the permanent memory PPI,
but the current dynamic implementations of the stack checking library
entrypoints for PEI_CORE and PEIM modules must not be used as-is.
So remove them, and update the readme accordingly.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Adds dynamic stack cookies in the form of copies of the entry
point libraries that use shared logic to update stack cookies
at runtime.
This relies on RDRAND on IA32/X64 and RNDR on AARCH64 to get a
random number to apply to the stack cookie on module entry point.
This simplifies the logic a platform must do to include stack
check functionality.
Signed-off-by: Oliver Smith-Denny <osde@microsoft.com>
In order to support a platform overriding StackCheckLibNull
provided by MdeLibs.dsc.inc, the CUSTOM_STACK_CHECK_LIB macro
is introduced. If this macro is defined, MdeLibs.dsc.inc will
not link StackCheckLibNull and it is expected that the platform
will link the version(s) of StackCheckLib that it requires.
The StackCheckLib README is also updated in this patch to
document the new macro and provide additional information.
Signed-off-by: Oliver Smith-Denny <osde@linux.microsoft.com>
StackCheckLib contains the required functionality for initializing
the stack cookie value, checking the value, and triggering an interrupt
when a mismatch occurs. The stack cookie is a random value placed on the
stack between the stack variables and the return address so that
continuously writing past the stack variables will cause the stack cookie
to be overwritten. Before the function returns, the stack cookie value
will be checked and if there is a mismatch then StackCheckLib handles the
failure.
Because UEFI doesn't use the C runtime libraries provided by MSVC, the
stack check code is written in assembly within this library. GCC and
Clang compilers have built-in support for stack cookie checking, so this
library only handles failures.
Signed-off-by: Oliver Smith-Denny <osde@linux.microsoft.com>
