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Multiple fixes for ModeSelect (#1405) 

* Allow 'empty' ModeSelect6

tl;dr

Treat a computed length of 0 as `has_valid_page_code`.

Details:

The SRM console (aka 'BIOS') of DEC Alpha sends an empty
ModeSelect6 with the following data:
~~~
ModeSelect6, CDB $151000000c00
~~~

That makes 12 byte(s) as follows
~~~
  0  1  2  3   4   5  6  7   8   9 10 11
 00 00 00 08  00  00 00 00  00  00 02 00
~~~

decoding it (accoring to [1], Section 8.3.3, Table 94) gives us

Mode Data Length 0
Medium Type      0
Device-specific  0
Block desc len   8

Density Code     0
Number of blks   0
Reserved         0
Block length     512

`scsi_command_util::ModeSelect` computes
~~~
offset = 4 + buf[3];
~~~

giving 12 and

~~~
length -= offset;
~~~

giving 0.

Thus it never enters the `while` loop and `has_valid_page_code` stays
`false`, raising an error.

[1] [Small Computer System Interface - 2 rev 10L.pdf](https://dn790004.ca.archive.org/0/items/SCSISpecificationDocumentsSCSIDocuments/Small%20Computer%20System%20Interface%20-%202%20rev%2010L.pdf)

Signed-off-by: Klaus Kämpf <kkaempf@gmail.com>

* Allow ModeSelect with page code 1

OpenVMS Alpha (the operating system, not the SRM BIOS) uses
ModeSelect6 with a page code of 1.

The semantics are unknown, just accepting it works for me.

Signed-off-by: Klaus Kämpf <kkaempf@gmail.com>

* Fix page length computation in ModeSelect

tl;dr

The 'skip to next ModeSelect page' computation was off-by-one, either not
taking the page code itself into account or missing the fact that the
page length is given as `n - 1`.

Fix:

Add 1 to the computed length.

Details:

OpenVMS Alpha sends a ModeSelect6 as follows
~~~
command:

ModeSelect6, CDB $151000001900

payload:

 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
00 00 00 08 00 00 00 00 00 00 02 00 01 0a 24 00 00 00 00 00 00 00 00 00 00
~~~

This translates to (accoring to [1], Section 8.3.3)

~~~
Mode Data Length 0
Medium Type      0
Device-specific  0
Block desc len   8
~~~

with the following offset / length computation _before_ the `while` loop
~~~
offset = 12
length = 13
~~~

The first payload section is
~~~
 4  5  6  7  8  9 10 11
00 00 00 00 00 00 02 00
~~~

translating to

~~~
Density Code     0
Number of blks   0
Reserved         0
Block length   0x200 512
~~~

Then follows a pagecode 1 as
~~~
12 13 14 15 16 17 18 19 20 21 22 23 24
01 0a 24 00 00 00 00 00 00 00 00 00 00
~~~

translating to
~~~~
Page code        1
Page length -1  10
Mode parameters 24 00 00 00 00 00 00 00 00 00 00
~~~

computing (inside the `while` loop, as `// Advance to the next page`)

~~~
size =  10 + 2 = 12
~~~

followed by new `offset` and `length` values

~~~
offset = 25
length = 1
~~~

So it stays in the `while` loop (and has a larger-than-buffer `offset`
value)

Signed-off-by: Klaus Kämpf <kkaempf@gmail.com>
This commit is contained in:
Klaus Kämpf 2024-01-07 07:06:35 +01:00 committed by GitHub
parent 256650908b
commit ad5eae93e7
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 31 additions and 5 deletions
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9
cpp/devices/scsi_command_util.cpp
View File

@ -40,7 +40,8 @@ string scsi_command_util::ModeSelect(scsi_command cmd, cdb_t cdb, span<const uin
}
length -= offset;
bool has_valid_page_code = false;
// treat zero length as valid
bool has_valid_page_code = (length == 0);
// Parse the pages
while (length > 0) {
@ -62,6 +63,10 @@ string scsi_command_util::ModeSelect(scsi_command cmd, cdb_t cdb, span<const uin
has_valid_page_code = true;
}
else if (page == 0x01) {
// OpenVMS Alpha 7.3 uses this
has_valid_page_code = true;
}
else {
stringstream s;
s << "Unknown MODE SELECT page code: $" << setfill('0') << setw(2) << hex << page;
@ -71,7 +76,7 @@ string scsi_command_util::ModeSelect(scsi_command cmd, cdb_t cdb, span<const uin
// Advance to the next page
const int size = buf[offset + 1] + 2;
length -= size;
length -= size + 1;
offset += size;
}

27
cpp/test/scsi_command_util_test.cpp
View File

@ -46,6 +46,11 @@ TEST(ScsiCommandUtilTest, ModeSelect6)
Property(&scsi_exception::get_asc, asc::invalid_field_in_parameter_list))))
<< "Unsupported page 0 was not rejected";
// Page 1
buf[12] = 0x01;
EXPECT_NO_THROW(ModeSelect(scsi_command::eCmdModeSelect6, cdb, buf, LENGTH, 512))
<< "Page 1 is supported";
// Page 3 (Format Device Page)
buf[12] = 0x03;
EXPECT_THAT([&] { ModeSelect(scsi_command::eCmdModeSelect6, cdb, buf, LENGTH, 512); },
@ -62,7 +67,25 @@ TEST(ScsiCommandUtilTest, ModeSelect6)
Property(&scsi_exception::get_asc, asc::invalid_field_in_parameter_list))))
<< "Not enough command parameters";
EXPECT_FALSE(ModeSelect(scsi_command::eCmdModeSelect6, cdb, buf, LENGTH, 512).empty());
// check length computation
buf[3] = 8;
buf[10] = 2;
buf[12] = 1;
buf[13] = 10;
buf[14] = 0x24;
buf[24] = 0;
EXPECT_NO_THROW(ModeSelect(scsi_command::eCmdModeSelect6, cdb, buf, LENGTH, 512))
<< "Multi-page length computation";
// check length computation
buf[3] = 8;
buf[10] = 12;
buf[12] = 0;
buf[13] = 0;
buf[14] = 0;
buf[24] = 0;
EXPECT_NO_THROW(ModeSelect(scsi_command::eCmdModeSelect6, cdb, buf, 12, 512))
<< "Empty ModeSelect6";
}
TEST(ScsiCommandUtilTest, ModeSelect10)
@ -111,8 +134,6 @@ TEST(ScsiCommandUtilTest, ModeSelect10)
Property(&scsi_exception::get_sense_key, sense_key::illegal_request),
Property(&scsi_exception::get_asc, asc::invalid_field_in_parameter_list))))
<< "Not enough command parameters";
EXPECT_FALSE(ModeSelect(scsi_command::eCmdModeSelect10, cdb, buf, LENGTH, 512).empty());
}
TEST(ScsiCommandUtilTest, EnrichFormatPage)