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netboot: Add longer kernel command lines support

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Since Linux commit 5ecb2da660ab ("s390: support command lines longer
than 896 bytes") the s390x kernel supports longer command lines than 896
bytes. The indication of the maximum size is stored in a new field at
address 0x10430, older kernels without the support store a value of 0
there so in that case fallback to the old maximum length of 896.

In addition, use the checked size as limit to copy in the 'dd' call.
This prevents Linux kernel corruption in case the parmline has changed
in between.

Fixes: https://github.com/ibm-s390-linux/s390-tools/issues/194
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
This commit is contained in:
Marc Hartmayer
2025-11-10 16:17:25 +00:00
committed by Jan Höppner
parent b29e824923
commit 128e5f86fe
1 changed files with 27 additions and 6 deletions
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33
netboot/mk-s390image
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@@ -21,8 +21,9 @@
# Offsets
OFFS_INITRD_START_BYTES=66568
OFFS_INITRD_SIZE_BYTES=66576
OFFS_COMMANDLINE_MAX_SIZE_BYTES=66608
OFFS_COMMANDLINE_BYTES=66688
MAX_PARMFILE_SIZE=896
LEGACY_MAX_PARMFILE_SIZE=896
# Variables
cmd=$(basename -- "$0")
@@ -87,6 +88,25 @@ dec2be64()
printf '%b' "$b"
}
max_kernel_cmdline_size()
{
local __kernel=$1 size v
size_be="$(od -A n -j "${OFFS_COMMANDLINE_MAX_SIZE_BYTES}" -N 8 -t uL -- "$__kernel")"
# If little endian then swap bytes
if (("$(printf '\1' | od -dAn)" == 1)); then
v="$(printf '%016x0' "$size_be")"
size="0x${v:14:2}${v:12:2}${v:10:2}${v:8:2}${v:6:2}${v:4:2}${v:2:2}${v:0:2}"
else
size="$size_be"
fi
if ((size == 0)); then
size="${LEGACY_MAX_PARMFILE_SIZE}"
fi
# Use arithmetic expression to remove leading and trailing whitespace.
printf '%s' "$((size))"
}
# Do the image build
dobuild()
{
@@ -137,16 +157,17 @@ dobuild()
# set cmdline
if [ "$parmfile" != "" ]
then
max_parmfile_size=$(max_kernel_cmdline_size "$kernel")
parmfile_size=$(du -b -L -- "$parmfile" | cut -f1)
if [ "$parmfile_size" -le $MAX_PARMFILE_SIZE ]
if (( parmfile_size <= max_parmfile_size ));
then
# Clear any previous parameters
dd seek=$OFFS_COMMANDLINE_BYTES bs=1 count=$MAX_PARMFILE_SIZE \
dd seek=$OFFS_COMMANDLINE_BYTES bs=1 count="$max_parmfile_size" \
if=/dev/zero of="$image" conv=notrunc status=none
dd seek=$OFFS_COMMANDLINE_BYTES bs=1 if="$parmfile" \
of="$image" conv=notrunc status=none
dd seek=$OFFS_COMMANDLINE_BYTES bs=1 count="$parmfile_size" \
if="$parmfile" of="$image" conv=notrunc status=none
else
echo "$cmd: Size $parmfile_size of $parmfile exceeds command line limit of $MAX_PARMFILE_SIZE" >&2
echo "$cmd: Size $parmfile_size of $parmfile exceeds command line limit of $max_parmfile_size bytes" >&2
return 1
fi
fi