Juergen Gross
2022-Sep-15 06:59 UTC
[PATCH v2 1/1] x86/paravirt: write paravirt ident function in assembly
On 14.09.22 18:21, Bill Wendling wrote:> The ZERO_CALL_USED_REGS feature may zero out caller-saved registers > before returning. However, alternate code may call this function without > first saving %[re]di, because the proper clobbers aren't taken into > account. > > This shows up in spurious_kernel_fault() where the "pte_offset_kernel()" > call results in this assembly code: > > .Ltmp151: > #APP > # ALT: oldnstr > .Ltmp152: > .Ltmp153: > .Ltmp154: > .section .discard.retpoline_safe,"", at progbits > .quad .Ltmp154 > .text > > callq *pv_ops+536(%rip) > > .Ltmp155: > .section .parainstructions,"a", at progbits > .p2align 3, 0x0 > .quad .Ltmp153 > .byte 67 > .byte .Ltmp155-.Ltmp153 > .short 1 > .text > .Ltmp156: > # ALT: padding > .zero (-(((.Ltmp157-.Ltmp158)-(.Ltmp156-.Ltmp152))>0))*((.Ltmp157-.Ltmp158)-(.Ltmp156-.Ltmp152)),144 > .Ltmp159: > .section .altinstructions,"a", at progbits > .Ltmp160: > .long .Ltmp152-.Ltmp160 > .Ltmp161: > .long .Ltmp158-.Ltmp161 > .short 33040 > .byte .Ltmp159-.Ltmp152 > .byte .Ltmp157-.Ltmp158 > .text > > .section .altinstr_replacement,"ax", at progbits > # ALT: replacement 1 > .Ltmp158: > movq %rdi, %rax > .Ltmp157: > .text > #NO_APP > .Ltmp162: > testb $-128, %dil > > The %dil register was zeroed out by the call to "*pv_ops+536(%rip)". > > In general, the _paravirt_ident_64() function appears like it shouldn't > have any instrumentation or other modifications applied to it. Thus just > write it in assembly to avoid having to continually modify it whenever a > new feature comes along. > > Link: https://github.com/KSPP/linux/issues/192 > Cc: Kees Cook <keescook at chromium.org> > Cc: Nick Desaulniers <ndesaulniers at google.com> > Cc: Juergen Gross <jgross at suse.com> > Cc: "Srivatsa S. Bhat (VMware)" <srivatsa at csail.mit.edu> > Cc: Alexey Makhalov <amakhalov at vmware.com> > Cc: Thomas Gleixner <tglx at linutronix.de> > Cc: Ingo Molnar <mingo at redhat.com> > Cc: Borislav Petkov <bp at alien8.de> > Cc: Dave Hansen <dave.hansen at linux.intel.com> > Cc: "H. Peter Anvin" <hpa at zytor.com> > Cc: VMware PV-Drivers Reviewers <pv-drivers at vmware.com> > Cc: x86 at kernel.org > Cc: virtualization at lists.linux-foundation.org > Cc: linux-kernel at vger.kernel.org > Cc: llvm at lists.linux.dev > Signed-off-by: Bill Wendling <morbo at google.com> > Suggested-by: Peter Zijlstra <peterz at infradead.org> > Reported-and-tested-by: Nathan Chancellor <nathan at kernel.org>Reviewed-by: Juergen Gross <jgross at suse.com> Juergen -------------- next part -------------- A non-text attachment was scrubbed... Name: OpenPGP_0xB0DE9DD628BF132F.asc Type: application/pgp-keys Size: 3098 bytes Desc: OpenPGP public key URL: <http://lists.linuxfoundation.org/pipermail/virtualization/attachments/20220915/1881fba6/attachment-0001.bin> -------------- next part -------------- A non-text attachment was scrubbed... Name: OpenPGP_signature Type: application/pgp-signature Size: 495 bytes Desc: OpenPGP digital signature URL: <http://lists.linuxfoundation.org/pipermail/virtualization/attachments/20220915/1881fba6/attachment-0001.sig>