On Sat, Apr 17, 2021 at 4:37 AM Peter Zijlstra <pet...@infradead.org> wrote: > > On Fri, Apr 16, 2021 at 01:38:38PM -0700, Sami Tolvanen wrote: > > From: Kees Cook <keesc...@chromium.org> > > > > Instead of using inline asm for the int3 selftest (which confuses the > > Clang's ThinLTO pass), this restores the C function but disables KASAN > > (and tracing for good measure) to keep the things simple and avoid > > unexpected side-effects. This attempts to keep the fix from commit > > ecc606103837 ("x86/alternatives: Fix int3_emulate_call() selftest stack > > corruption") without using inline asm. > > > > Signed-off-by: Kees Cook <keesc...@chromium.org> > > Signed-off-by: Sami Tolvanen <samitolva...@google.com> > > --- > > arch/x86/kernel/alternative.c | 21 ++++----------------- > > 1 file changed, 4 insertions(+), 17 deletions(-) > > > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > > index 6974b5174495..669a23454c09 100644 > > --- a/arch/x86/kernel/alternative.c > > +++ b/arch/x86/kernel/alternative.c > > @@ -496,23 +496,10 @@ extern struct paravirt_patch_site > > __start_parainstructions[], > > * > > * See entry_{32,64}.S for more details. > > */ > > - > > -/* > > - * We define the int3_magic() function in assembly to control the calling > > - * convention such that we can 'call' it from assembly. > > - */ > > - > > -extern void int3_magic(unsigned int *ptr); /* defined in asm */ > > - > > -asm ( > > -" .pushsection .init.text, \"ax\", @progbits\n" > > -" .type int3_magic, @function\n" > > -"int3_magic:\n" > > -" movl $1, (%" _ASM_ARG1 ")\n" > > -" ret\n" > > -" .size int3_magic, .-int3_magic\n" > > -" .popsection\n" > > -); > > +static void __init __no_sanitize_address notrace int3_magic(unsigned int > > *ptr) > > +{ > > + *ptr = 1; > > +} > > I really don't like this. the compiler is free to mess this up in all > sorts of ways. > > The problem is that the call-site does not respect the regular calling > convention, so calling a regular C function is just asking for trouble, > which is why it ended up being asm, then we fully control the calling > convention.
Ack. The problem here is that we can't declare an extern static function in C. How would you feel about making int3_magic a global instead to match the C declaration? Sami