From 9d7de2aa8b41407bc96d89a80dc1fd637d389d42 Mon Sep 17 00:00:00 2001 From: Brian Gerst Date: Thu, 23 Jan 2025 14:07:40 -0500 Subject: x86/percpu/64: Use relative percpu offsets The percpu section is currently linked at absolute address 0, because older compilers hard-coded the stack protector canary value at a fixed offset from the start of the GS segment. Now that the canary is a normal percpu variable, the percpu section does not need to be linked at a specific address. x86-64 will now calculate the percpu offsets as the delta between the initial percpu address and the dynamically allocated memory, like other architectures. Note that GSBASE is limited to the canonical address width (48 or 57 bits, sign-extended). As long as the kernel text, modules, and the dynamically allocated percpu memory are all in the negative address space, the delta will not overflow this limit. Signed-off-by: Brian Gerst Signed-off-by: Ingo Molnar Reviewed-by: Ard Biesheuvel Reviewed-by: Uros Bizjak Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250123190747.745588-9-brgerst@gmail.com --- init/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'init') diff --git a/init/Kconfig b/init/Kconfig index d0d021b3fa3b..b5d9c0fa69f6 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1872,7 +1872,7 @@ config KALLSYMS_ALL config KALLSYMS_ABSOLUTE_PERCPU bool depends on KALLSYMS - default X86_64 && SMP + default n # end of the "standard kernel features (expert users)" menu -- cgit v1.2.3