Messages in this thread | | | Date | Tue, 14 Nov 2023 13:37:37 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v4 2/5] x86/alternative: add indirect call patching |
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On Mon, Oct 30, 2023 at 03:25:05PM +0100, Juergen Gross wrote: > + * Rewrite the "call BUG_func" replacement to point to the target of the > + * indirect pv_ops call "call *disp(%ip)". > + */ > +static int alt_replace_call(u8 *instr, u8 *insn_buff, struct alt_instr *a) > +{ > + void *target, *bug = &BUG_func; > + > + if (a->replacementlen != 5 || insn_buff[0] != CALL_INSN_OPCODE) { > + pr_err("Alternative: ALT_FLAG_CALL set for a non-call replacement instruction\n");
No need for the printk prefix.
> + pr_err(" Ignoring the flag for the instruction at %pS (%px)\n", instr, instr);
No ignoring - BUG
> + return 5; > + } > + > + if (a->instrlen != 6 || instr[0] != 0xff || instr[1] != 0x15) { > + pr_err("Alternative: ALT_FLAG_CALL set for unrecognized indirect call\n"); > + pr_err(" Not replacing the instruction at %pS (%px)\n", instr, instr); > + return -1;
Ditto.
> + } > + > +#ifdef CONFIG_X86_64 > + /* ff 15 00 00 00 00 call *0x0(%rip) */ > + target = *(void **)(instr + a->instrlen + *(s32 *)(instr + 2)); > +#else > + /* ff 15 00 00 00 00 call *0x0 */ > + target = *(void **)(*(s32 *)(instr + 2)); > +#endif > + if (!target) > + target = bug; > + > + /* (BUG_func - .) + (target - BUG_func) := target - . */ > + *(s32 *)(insn_buff + 1) += target - bug;
If I squint hard enough, this looks like it is replacing one call with another. We have a C macro alternative_call() which does exactly that. Why can't you define an asm version ALTERNATIVE_CALL and use it instead of using adding a new flag? We have 16 possible ones in total.
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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