Re: [Xen-devel] [PATCH] EFI: Fix getting EFI variable list on some systems

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.03.15 at 17:47, <ross.lagerwall@xxxxxxxxxx> wrote:
> Copy the entire output buffer to the guest because it may contain data beyond
> the output size that the firmware requires on a subsequent
> GetNextVariableName() call (e.g. a NULL character).
> 
> The spec requires that on each call, "the previous results" be passed in.
> 
> Without this change, the following (simplified) sequence would occur:
> GetNextVariableName: in \0, out AdminPw\0, size 7
> GetNextVariableName: in AdminPw\0, out UserPw\0, size 6
> GetNextVariableName: in UserPww\0, NOT FOUND

As such behavior is outside the specification, please name the system
needing this workaround: The runtime services function is documented
to update *VariableNameSize only upon EFI_BUFFER_TOO_SMALL. A
code comment would also seem to be on order, as otherwise people
like me might be tempted to undo this again, as it's sub-optimal code
for spec conforming firmware.

And to save me from having to do an incremental patch on top, you
may want to consider switching to __copy_to_user() at once.

Jan


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