From: Joerg Roedel <jroedel@xxxxxxx> When stack-protector is enabled a valid GS_BASE is needed before calling any C code function, because the stack canary is loaded from per-cpu data. Signed-off-by: Joerg Roedel <jroedel@xxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Link: https://lore.kernel.org/r/20200724160336.5435-31-joro@xxxxxxxxxx --- arch/x86/kernel/head64.c | 7 +++++++ arch/x86/kernel/head_64.S | 8 ++++++++ 2 files changed, 15 insertions(+) diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index 8c82be44be94..b0ab5627900b 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -36,6 +36,7 @@ #include <asm/microcode.h> #include <asm/kasan.h> #include <asm/fixmap.h> +#include <asm/realmode.h> /* * Manage page tables very early on. @@ -513,6 +514,8 @@ void __init x86_64_start_reservations(char *real_mode_data) */ void __head startup_64_setup_env(unsigned long physbase) { + unsigned long gsbase; + /* Load GDT */ startup_gdt_descr.address = (unsigned long)fixup_pointer(startup_gdt, physbase); native_load_gdt(&startup_gdt_descr); @@ -521,4 +524,8 @@ void __head startup_64_setup_env(unsigned long physbase) asm volatile("movl %%eax, %%ds\n" "movl %%eax, %%ss\n" "movl %%eax, %%es\n" : : "a"(__KERNEL_DS) : "memory"); + + /* Setup GS_BASE - needed for stack protector */ + gsbase = (unsigned long)fixup_pointer((void *)initial_gs, physbase); + __wrmsr(MSR_GS_BASE, (u32)gsbase, (u32)(gsbase >> 32)); } diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 2b2e91627221..800053219054 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -78,6 +78,14 @@ SYM_CODE_START_NOALIGN(startup_64) call startup_64_setup_env popq %rsi + /* + * Setup %gs here already to make stack-protector work - it needs to be + * setup again after the switch to kernel addresses. The address read + * from initial_gs is a kernel address, so it needs to be adjusted first + * for the identity mapping. + */ + movl $MSR_GS_BASE,%ecx + /* Now switch to __KERNEL_CS so IRET works reliably */ pushq $__KERNEL_CS leaq .Lon_kernel_cs(%rip), %rax -- 2.28.0 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
