The most common and most likely answer to this crossword clue is the 8 letter word CONFIRMS
I've seen this crossword clue in The Times
C
O
N
F
I
R
M
S
More clues leading to the result CONFIRMS
Buddy explains!

The straight part
We know that "Upholds" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case upholds = confirms.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CONFIRMS mean?
CONFIRMS verb- To strengthen; to make firm or resolute.
- To administer the sacrament of confirmation on (someone).
- To assure the accuracy of previous statements.