From: Nick Desaulniers ndesaulniers@google.com
commit cbe8ded48b939b9d55d2c5589ab56caa7b530709 upstream.
The assertion added to verify the difference in bits set of the addresses of srso_untrain_ret_alias() and srso_safe_ret_alias() would fail to link in LLVM's ld.lld linker with the following error:
ld.lld: error: ./arch/x86/kernel/vmlinux.lds:210: at least one side of the expression must be absolute ld.lld: error: ./arch/x86/kernel/vmlinux.lds:211: at least one side of the expression must be absolute
Use ABSOLUTE to evaluate the expression referring to at least one of the symbols so that LLD can evaluate the linker script.
Also, add linker version info to the comment about XOR being unsupported in either ld.bfd or ld.lld until somewhat recently.
Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation") Closes: https://lore.kernel.org/llvm/CA+G9fYsdUeNu-gwbs0+T6XHi4hYYk=Y9725-wFhZ7gJMsp... Reported-by: Nathan Chancellor nathan@kernel.org Reported-by: Daniel Kolesa daniel@octaforge.org Reported-by: Naresh Kamboju naresh.kamboju@linaro.org Suggested-by: Sven Volkinsfeld thyrc@gmx.net Signed-off-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Link: https://github.com/ClangBuiltLinux/linux/issues/1907 Link: https://lore.kernel.org/r/20230809-gds-v1-1-eaac90b0cbcc@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/vmlinux.lds.S | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)
--- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -529,11 +529,17 @@ INIT_PER_CPU(irq_stack_backing_store);
#ifdef CONFIG_CPU_SRSO /* - * GNU ld cannot do XOR so do: (A | B) - (A & B) in order to compute the XOR + * GNU ld cannot do XOR until 2.41. + * https://sourceware.org/git/?p=binutils-gdb.git%3Ba=commit%3Bh=f6f78318fca803... + * + * LLVM lld cannot do XOR until lld-17. + * https://github.com/llvm/llvm-project/commit/fae96104d4378166cbe5c875ef8ed808... + * + * Instead do: (A | B) - (A & B) in order to compute the XOR * of the two function addresses: */ -. = ASSERT(((srso_untrain_ret_alias | srso_safe_ret_alias) - - (srso_untrain_ret_alias & srso_safe_ret_alias)) == ((1 << 2) | (1 << 8) | (1 << 14) | (1 << 20)), +. = ASSERT(((ABSOLUTE(srso_untrain_ret_alias) | srso_safe_ret_alias) - + (ABSOLUTE(srso_untrain_ret_alias) & srso_safe_ret_alias)) == ((1 << 2) | (1 << 8) | (1 << 14) | (1 << 20)), "SRSO function pair won't alias"); #endif