On 19/03/2025 12:39 pm, Jan Beulich wrote:
> On 19.03.2025 13:12, Andrew Cooper wrote:
>> On 19/03/2025 11:18 am, Jan Beulich wrote:
>>> As per observation in practice, initrd->cmdline_pa is not normally zero.
>>> Hence so far we always appended at least one byte. That alone may
>>> already render insufficient the "allocation" made by find_memory().
>>> Things would be worse when there's actually a (perhaps long) command
>>> line.
>>>
>>> Skip setup when the command line is empty. Amend the "allocation" size
>>> by padding and actual size of module command line.
>>>
>>> Fixes: 0ecb8eb09f9f ("x86/pvh: pass module command line to dom0")
>>> Signed-off-by: Jan Beulich <jbeul...@suse.com>
>>>
>>> --- a/xen/arch/x86/hvm/dom0_build.c
>>> +++ b/xen/arch/x86/hvm/dom0_build.c
>>> @@ -712,7 +712,15 @@ static int __init pvh_load_kernel(
>>> * simplify it.
>>> */
>>> last_addr = find_memory(d, &elf, sizeof(start_info) +
>>> - (initrd ? ROUNDUP(initrd_len, PAGE_SIZE) +
>>> + (initrd ? ROUNDUP(ROUNDUP(initrd_len,
>>> + elf_64bit(&elf) ? 8
>>> : 4) +
>>> + (initrd->cmdline_pa &&
>>> + strlen(__va(initrd->
>>> + cmdline_pa))
>>> + ? strlen(__va(initrd->
>>> + cmdline_pa))
>>> + 1
>>> + : 0),
>>> + PAGE_SIZE) +
>>> sizeof(mod)
>>> : 0) +
>>> (cmdline ? ROUNDUP(strlen(cmdline) + 1,
>> This piece of logic was already bad, but this is rather worse.
>>
>> One patch I made while doing the boot module work is:
>>
>> diff --git a/xen/arch/x86/hvm/dom0_build.c b/xen/arch/x86/hvm/dom0_build.c
>> index 6a4453103a9a..7292ddd07276 100644
>> --- a/xen/arch/x86/hvm/dom0_build.c
>> +++ b/xen/arch/x86/hvm/dom0_build.c
>> @@ -654,6 +654,7 @@ static int __init pvh_load_kernel(
>> const char *cmdline = image->cmdline_pa ? __va(image->cmdline_pa) :
>> NULL;
>> struct elf_binary elf;
>> struct elf_dom_parms parms;
>> + size_t metadata_len;
>> paddr_t last_addr;
>> struct hvm_start_info start_info = { 0 };
>> struct hvm_modlist_entry mod = { 0 };
>> @@ -711,13 +712,16 @@ static int __init pvh_load_kernel(
>> * split into smaller allocations, done as a single region in order to
>> * simplify it.
>> */
>> - last_addr = find_memory(d, &elf, sizeof(start_info) +
>> - (initrd ? ROUNDUP(initrd_len, PAGE_SIZE) +
>> - sizeof(mod)
>> - : 0) +
>> - (cmdline ? ROUNDUP(strlen(cmdline) + 1,
>> - elf_64bit(&elf) ? 8 : 4)
>> - : 0));
>> + metadata_len = sizeof(start_info);
>> +
>> + if ( initrd )
>> + metadata_len += sizeof(mod) + ROUNDUP(initrd_len, PAGE_SIZE);
>> +
>> + if ( cmdline )
>> + metadata_len += ROUNDUP(strlen(cmdline) + 1,
>> + elf_64bit(&elf) ? 8 : 4);
>> +
>> + last_addr = find_memory(d, &elf, metadata_len);
>> if ( last_addr == INVALID_PADDR )
>> {
>> printk("Unable to find a memory region to load initrd and
>> metadata\n");
>>
>>
>> which I think I ought to submit as a prerequisite to this, after which
>> your logic squashed on the RHS now becomes an expansion of the `if (
>> initrd )`.
> Yes please.
https://lore.kernel.org/xen-devel/20250319171346.19478-1-andrew.coop...@citrix.com/T/#u
> Another thing I was considering to put in a local variable is the
> repeated "elf_64bit(&elf) ? 8 : 4". If that sounds okay, I can make that
> a(nother) pre-patch to mine.
Yeah, I was thinking the same. There's a related expression in
elf_round_up(), so it might be worth having a macro in
include/xen/libelf.h for elf_ptr_size() or so.
~Andrew
