On 22 Apr 2020, at 15:35, Andi Kleen ak@linux.intel.com wrote:
Thanks good catch.
if (cmdline_find_option(boot_command_line, "clearcpuid", arg,
sizeof(arg)) &&get_option(&argptr, &bit) &&bit >= 0 &&bit < NCAPINTS * 32)setup_clear_cpu_cap(bit);
sizeof(arg))) {/* cpuid bit numbers are mostly three digits */enum { nints = sizeof(arg)/(3+1) + 1 };Not sure what the digits have to do with the stack space of an int array.
We should have enough stack to afford some more than 8.
sizeof(arg) == 32; room enough for eight three-digit with their trailing commas. If sizeof(arg) == 1024 instead then there'd be more than enough room to remove every single feature. TBH, 512 is more than enough for the 89 flags I have listed on this machine I'm looking at here. I'll grow sizeof(arg) and nints accordingly.
Would be good to have a warning if the arguments are longer.
Yes, I should definitely do that -- coming to a V2 soon.
Maybe it would be simpler to fix the early arg parser to allow multiple instances again? That would also avoid the limit, and keep everything compatible.
I did wonder about that. However, cmdline_find_option() is specifically documented as
* Find a non-boolean option (i.e. option=argument). In accordance with * standard Linux practice, if this option is repeated, this returns the * last instance on the command line.
And since that appeared in 2017 I decided to stick with the new-fangled interface :) This is a little-used feature; I'm not sure it's worth the effort of parsing the command line for the old style. What do you think?
jch
-Andi
int i, bits[nints];get_options(arg, nints, bits);for (i = 1; i <= bits[0]; i++) {if (bits[i] >= 0 && bits[i] < NCAPINTS * 32)setup_clear_cpu_cap(bits[i]);}- }
}
/*
2.25.3