Messages in this thread | | | Date | Wed, 15 Nov 2017 09:41:00 +0100 | From | Ingo Molnar <> | Subject | Re: [RESEND PATCH v2 4/4] x86/umip: Warn if UMIP-protected instructions are used |
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* Ricardo Neri <ricardo.neri-calderon@linux.intel.com> wrote:
> > > + 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.
This is still very fragile.
The right solution would be to make umip_pr_warn() a varargs helper function, so that you can just use it to print things the usual way. I'd also use a __attribute__((format(printf))) specification to get good build-time warnings.
Thanks,
Ingo
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