Messages in this thread | | | Date | Thu, 25 Feb 2021 13:16:30 -0800 | From | Sean Christopherson <> | Subject | Re: [RFC 1/6] vdso/extable: fix calculation of base |
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On Wed, Feb 24, 2021, Nadav Amit wrote: > From: Nadav Amit <namit@vmware.com> > > Apparently, the assembly considers __ex_table as the location when the > pushsection directive was issued. Therefore when there is more than a > single entry in the vDSO exception table, the calculations of the base > and fixup are wrong. > > Fix the calculations of the expected fault IP and new IP by adjusting > the base after each entry. > > Cc: Andy Lutomirski <luto@kernel.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Sean Christopherson <seanjc@google.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Borislav Petkov <bp@alien8.de> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: x86@kernel.org > Signed-off-by: Nadav Amit <namit@vmware.com> > --- > arch/x86/entry/vdso/extable.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/entry/vdso/extable.c b/arch/x86/entry/vdso/extable.c > index afcf5b65beef..c81e78636220 100644 > --- a/arch/x86/entry/vdso/extable.c > +++ b/arch/x86/entry/vdso/extable.c > @@ -32,7 +32,7 @@ bool fixup_vdso_exception(struct pt_regs *regs, int trapnr, > nr_entries = image->extable_len / (sizeof(*extable)); > extable = image->extable; > > - for (i = 0; i < nr_entries; i++) { > + for (i = 0; i < nr_entries; i++, base += sizeof(*extable)) {
It's been literally years since I wrote this code, but I distinctly remember the addresses being relative to the base. I also remember testing multiple entries, but again, that was a long time ago.
Assuming things have changed, or I was flat out wrong, the comment above the macro magic should also be updated.
/* * Inject exception fixup for vDSO code. Unlike normal exception fixup, * vDSO uses a dedicated handler the addresses are relative to the overall * exception table, not each individual entry. */
> if (regs->ip == base + extable[i].insn) { > regs->ip = base + extable[i].fixup; > regs->di = trapnr; > -- > 2.25.1 >
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