Re: [PATCH Part1 v5 23/38] x86/head/64: set up a startup %gs for stack protector
From: Michael Roth <hidden>
Date: 2021-08-25 17:15:19
Also in:
kvm, linux-efi, linux-mm, lkml, platform-driver-x86
On Wed, Aug 25, 2021 at 05:07:26PM +0200, Joerg Roedel wrote:
On Fri, Aug 20, 2021 at 10:19:18AM -0500, Brijesh Singh wrote:quoted
void __head startup_64_setup_env(unsigned long physbase) { + u64 gs_area = (u64)fixup_pointer(startup_gs_area, physbase); +This breaks as soon as the compiler decides that startup_64_setup_env() needs stack protection too.
Good point.
quoted hunk ↗ jump to hunk
And the startup_gs_area is also not needed, there is initial_gs for that. What you need is something along these lines (untested):diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index d8b3ebd2bb85..3c7c59bc9903 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S@@ -65,6 +65,16 @@ SYM_CODE_START_NOALIGN(startup_64) leaq (__end_init_task - FRAME_SIZE)(%rip), %rsp leaq _text(%rip), %rdi + + movl $MSR_GS_BASE, %ecx + movq initial_gs(%rip), %rax + movq $_text, %rdx + subq %rdx, %rax + addq %rdi, %rax + movq %rax, %rdx + shrq $32, %rdx + wrmsr + pushq %rsi call startup_64_setup_env popq %rsiIt loads the initial_gs pointer, applies the fixup on it and loads it into MSR_GS_BASE.
This seems to do the trick, and is probably closer to what the 32-bit version would look like. Thanks for the suggestion!