[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] x86/PVH: account for module command line length
On Wed, Mar 19, 2025 at 12:12:22PM +0000, 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 <jbeulich@xxxxxxxx> > > > > --- 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? Yes please, I was going to ask Jan to break that chain of ?: operators as it's impossible to read. Thanks, Roger.
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