Messages in this thread | | | Date | Tue, 14 Nov 2017 18:56:03 -0800 | From | Ricardo Neri <> | Subject | Re: [RESEND PATCH v2 4/4] x86/umip: Warn if UMIP-protected instructions are used |
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On Tue, Nov 14, 2017 at 08:34:08AM +0100, Ingo Molnar wrote: > > * Ricardo Neri <ricardo.neri-calderon@linux.intel.com> wrote: > > > +const char * const umip_insns[5] = { > > + [UMIP_INST_SGDT] = "sgdt", > > + [UMIP_INST_SIDT] = "sidt", > > + [UMIP_INST_SMSW] = "smsw", > > + [UMIP_INST_SLDT] = "sldt", > > + [UMIP_INST_STR] = "str", > > +}; > > Sigh ...
It made sense to me to capitalize code and changelogs but keep the printed warnings in lower case. Thus, the format would look like:
umip: smsw instruction cannot be used by applications.
I do see that this could be confusing with STR. I will capitalize these as well. > > > +/* > > + * If you change these strings, ensure that buffers using them are sufficiently > > + * large. > > + */ > > +static const char umip_warn_use[] = "cannot be used by applications."; > > +static const char umip_warn_emu[] = "For now, expensive software emulation returns result."; > > Please use the string literals directly, don't add an extra obfuscation layer. > > Plus: > > > + unsigned char buf[MAX_INSN_SIZE], warn[128]; > > > + snprintf(warn, sizeof(warn), "%s %s", umip_insns[umip_inst], > > + umip_warn_use); > > This is incredibly fragile against future buffer overflows, and warning about it > in comments does not make it less fragile!
I need to concatenate the instruction mnemonic with the a string. Does something like this is more acceptable?
unsigned char warn[50];
...
strcpy(warn, umip_insns[umip_inst]); strcat(warn, " instruction cannot be used by applications."); umip_pr_warn(regs, warn, 0);
In this manner I use the string literal directly but I still have a buffer that might overflow. Code looks more clear to me. I could #defines for the string lengths or set a maximum length.
Thanks and BR, Ricardo
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