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 )`.
Thoughts?
~Andrew
