From: Damian Tometzki Sent: November 11, 2018 at 7:11:42 PM GMT > To: Nadav Amit <[email protected]> > Cc: Ingo Molnar <[email protected]>, [email protected]>, > [email protected]>, H. Peter Anvin <[email protected]>, Thomas Gleixner > <[email protected]>, Borislav Petkov <[email protected]>, Dave Hansen > <[email protected]>, Andy Lutomirski <[email protected]>, Kees Cook > <[email protected]>, Peter Zijlstra <[email protected]>, Dave Hansen > <[email protected]>, Masami Hiramatsu <[email protected]> > Subject: Re: [PATCH v4 06/10] x86/alternative: use temporary mm for text > poking > > > On Sa, 10. Nov 15:17, Nadav Amit wrote: >> text_poke() can potentially compromise the security as it sets temporary >> PTEs in the fixmap. These PTEs might be used to rewrite the kernel code >> from other cores accidentally or maliciously, if an attacker gains the >> ability to write onto kernel memory. >> >> Moreover, since remote TLBs are not flushed after the temporary PTEs are >> removed, the time-window in which the code is writable is not limited if >> the fixmap PTEs - maliciously or accidentally - are cached in the TLB. >> To address these potential security hazards, we use a temporary mm for >> patching the code. >> >> Finally, text_poke() is also not conservative enough when mapping pages, >> as it always tries to map 2 pages, even when a single one is sufficient. >> So try to be more conservative, and do not map more than needed. >> >> Cc: Andy Lutomirski <[email protected]> >> Cc: Kees Cook <[email protected]> >> Cc: Peter Zijlstra <[email protected]> >> Cc: Dave Hansen <[email protected]> >> Cc: Masami Hiramatsu <[email protected]> >> Signed-off-by: Nadav Amit <[email protected]> >> --- >> arch/x86/include/asm/fixmap.h | 2 - >> arch/x86/kernel/alternative.c | 112 +++++++++++++++++++++++++++------- >> 2 files changed, 89 insertions(+), 25 deletions(-) >> >> diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h >> index 50ba74a34a37..9da8cccdf3fb 100644 >> --- a/arch/x86/include/asm/fixmap.h >> +++ b/arch/x86/include/asm/fixmap.h >> @@ -103,8 +103,6 @@ enum fixed_addresses { >> #ifdef CONFIG_PARAVIRT >> FIX_PARAVIRT_BOOTMAP, >> #endif > > Hello Nadav, > > with the remove of FIX_TEXT_POKE1 and FIX_TEXT_POKE0 i get the following > build error: > > /home/damian/kernel/linux/arch/x86/xen/mmu_pv.c:2321:7: Fehler: > »FIX_TEXT_POKE0« nicht deklariert (erstmalige Verwendung in dieser Funktion); > meinten Sie »FIX_TBOOT_BASE«? > case FIX_TEXT_POKE0: > ^~~~~~~~~~~~~~ > FIX_TBOOT_BASE > /home/damian/kernel/linux/arch/x86/xen/mmu_pv.c:2321:7: Anmerkung: jeder > nicht deklarierte Bezeichner wird nur einmal für jede Funktion, in der er > vorkommt, gemeldet > /home/damian/kernel/linux/arch/x86/xen/mmu_pv.c:2322:7: Fehler: > »FIX_TEXT_POKE1« nicht deklariert (erstmalige Verwendung in dieser Funktion); > meinten Sie »FIX_TBOOT_BASE«? > case FIX_TEXT_POKE1: > ^~~~~~~~~~~~~~ > FIX_TBOOT_BASE
Thanks for letting me know. I’ll simply remove them in v5. Regards, Nadav
