diff options
| -rw-r--r-- | pkg/sentry/mm/pma.go | 41 |
1 files changed, 29 insertions, 12 deletions
diff --git a/pkg/sentry/mm/pma.go b/pkg/sentry/mm/pma.go index 9f4cc238f..05cdcd8ae 100644 --- a/pkg/sentry/mm/pma.go +++ b/pkg/sentry/mm/pma.go @@ -324,20 +324,37 @@ func (mm *MemoryManager) getPMAsInternalLocked(ctx context.Context, vseg vmaIter panic(fmt.Sprintf("pma %v needs to be copied for writing, but is not readable: %v", pseg.Range(), oldpma)) } } - // The majority of copy-on-write breaks on executable pages - // come from: - // - // - The ELF loader, which must zero out bytes on the last - // page of each segment after the end of the segment. - // - // - gdb's use of ptrace to insert breakpoints. - // - // Neither of these cases has enough spatial locality to - // benefit from copying nearby pages, so if the vma is - // executable, only copy the pages required. var copyAR hostarch.AddrRange - if vseg.ValuePtr().effectivePerms.Execute { + if vma := vseg.ValuePtr(); vma.effectivePerms.Execute { + // The majority of copy-on-write breaks on executable + // pages come from: + // + // - The ELF loader, which must zero out bytes on the + // last page of each segment after the end of the + // segment. + // + // - gdb's use of ptrace to insert breakpoints. + // + // Neither of these cases has enough spatial locality + // to benefit from copying nearby pages, so if the vma + // is executable, only copy the pages required. copyAR = pseg.Range().Intersect(ar) + } else if vma.growsDown { + // In most cases, the new process will not use most of + // its stack before exiting or invoking execve(); it is + // especially unlikely to return very far down its call + // stack, since async-signal-safety concerns in + // multithreaded programs prevent the new process from + // being able to do much. So only copy up to one page + // before and after the pages required. + stackMaskAR := ar + if newStart := stackMaskAR.Start - hostarch.PageSize; newStart < stackMaskAR.Start { + stackMaskAR.Start = newStart + } + if newEnd := stackMaskAR.End + hostarch.PageSize; newEnd > stackMaskAR.End { + stackMaskAR.End = newEnd + } + copyAR = pseg.Range().Intersect(stackMaskAR) } else { copyAR = pseg.Range().Intersect(maskAR) } |