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edu: fix DMA range upper bound check 

The edu_check_range function checks that start <= end1 < end2, where
end1 is the upper bound (exclusive) of the guest-supplied DMA range and
end2 is the upper bound (exclusive) of the device's allowed DMA range.
When the guest tries to transfer exactly DMA_SIZE (4096) bytes, end1
will be equal to end2, so the check fails and QEMU aborts with this
puzzling error message (newlines added for formatting):

  qemu: hardware error: EDU: DMA range
    0x0000000000040000-0x0000000000040fff out of bounds
   (0x0000000000040000-0x0000000000040fff)!

By checking end1 <= end2 instead, guests will be allowed to transfer
exactly 4096 bytes. It is not necessary to explicitly check for
start <= end1 because the previous two checks (within(addr, start, end2)
and end1 > addr) imply start < end1.

Fixes: b30934cb52 ("hw: misc, add educational driver", 2015-01-21)
Signed-off-by: Max Erenberg <merenber@uwaterloo.ca>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
master
Max Erenberg 2023-12-25 18:44:32 -05:00 committed by Michael Tokarev
parent 0c7ffc9771
commit 2c5107e1b4
1 changed files with 1 additions and 1 deletions
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2
hw/misc/edu.c
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@ -115,7 +115,7 @@ static void edu_check_range(uint64_t addr, uint64_t size1, uint64_t start,
uint64_t end2 = start + size2;
if (within(addr, start, end2) &&
end1 > addr && within(end1, start, end2)) {
end1 > addr && end1 <= end2) {
return;
}