Re: [RFC 1/6] vdso/extable: fix calculation of base
From: Sean Christopherson <seanjc@google.com>
Date: 2021-02-25 21:17:52
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On Wed, Feb 24, 2021, Nadav Amit wrote:
quoted hunk ↗ jump to hunk
From: Nadav Amit <redacted> 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 <redacted> 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 <redacted> --- 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