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SubjectRe: [PATCH v2 5/5] x86/head/64: Disable stack protection for head$(BITS).o
On Thu, Oct 08, 2020 at 03:16:23PM -0400, Arvind Sankar wrote:
> On 64-bit, the startup_64_setup_env() function added in
> 866b556efa12 ("x86/head/64: Install startup GDT")
> has stack protection enabled because of set_bringup_idt_handler().

Where? I don't see it.

I have

CONFIG_STACKPROTECTOR=y
# CONFIG_STACKPROTECTOR_STRONG is not set

and a __stack_chk_fail call is nowhere to be found in the resulting
head64.s file.

startup_64_setup_env:
# arch/x86/kernel/head64.c:91: return ptr - (void *)_text + (void *)physaddr;
leaq startup_gdt(%rdi), %rax #, tmp99
# arch/x86/kernel/head64.c:91: return ptr - (void *)_text + (void *)physaddr;
subq $_text, %rax #, tmp101
movq %rax, startup_gdt_descr+2(%rip) # tmp101, startup_gdt_descr.address
# ./arch/x86/include/asm/desc.h:209: asm volatile("lgdt %0"::"m" (*dtr));
#APP
# 209 "./arch/x86/include/asm/desc.h" 1
lgdt startup_gdt_descr(%rip) # startup_gdt_descr
# 0 "" 2
# arch/x86/kernel/head64.c:600: asm volatile("movl %%eax, %%ds\n"
#NO_APP
movl $24, %eax #, tmp102
#APP
# 600 "arch/x86/kernel/head64.c" 1
movl %eax, %ds
movl %eax, %ss
movl %eax, %es

# 0 "" 2
# arch/x86/kernel/head64.c:91: return ptr - (void *)_text + (void *)physaddr;
#NO_APP
leaq bringup_idt_table(%rdi), %r9 #, tmp105
leaq bringup_idt_descr(%rdi), %r8 #, tmp103
leaq vc_no_ghcb(%rdi), %rsi #, tmp107
# arch/x86/kernel/head64.c:91: return ptr - (void *)_text + (void *)physaddr;
subq $_text, %r9 #, _11
subq $_text, %r8 #, _8
subq $_text, %rsi #, tmp109
# arch/x86/kernel/head64.c:572: set_bringup_idt_handler(idt, X86_TRAP_VC, handler);
movq %r9, %rdi # _11,
call set_bringup_idt_handler.constprop.0 #
# arch/x86/kernel/head64.c:575: desc->address = (unsigned long)idt;
movq %r9, 2(%r8) # _11, MEM[(struct desc_ptr *)_8].address
# ./arch/x86/include/asm/desc.h:214: asm volatile("lidt %0"::"m" (*dtr));
#APP
# 214 "./arch/x86/include/asm/desc.h" 1
lidt (%r8) # MEM[(const struct desc_ptr *)_8]
# 0 "" 2
# arch/x86/kernel/head64.c:605: }
#NO_APP
ret

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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