In the Linux kernel, the following vulnerability has been resolved:
coresight: etm4x: fix underflow for usage of (nrseqstate – 1)
According to IHI006H Embedded Trace Macrocell Architecture
Specification[0], TRCSEQEVR is implemented only when
TRCIDR5.NUMSEQSTATE is 0b100, in which case n ranges from 0 to 2;
otherwise, TRCIDR5.NUMSEQSTATE is 0b000.
IOW, the number of usage in the initialisation or setting
TRCSEQEVR with drvdata->nrseqstate – 1 in the loop could make
underflow issue when TRCIDR5.NUMSEQSTATE is 0b000.
Therefore, introduce nr_seq_ctrls field and untie it from nrseqstate.
As part of this introduce ETM_MAX_SEQ_TRANSITIONS macro and
apply nr_seq_ctrls and above macro to TRCSEQEVR relevant fields setup.
