loader: Fix ELF relocation logic for Linux v6.17+ startup code layout

After Linux v6.17, the x86_64 kernel startup code moved from .head.text
to .init.text. Update the loader to check the lowest program header address
for relocation, not just the entry point, to handle both old and new kernels.

Co-authored-by: GitHub Copilot <copilot@microsoft.com>

Author: Naman Jain

vm/loader/src/elf.rs

@@ -133,9 +133,37 @@ where
     }
 
     let e_entry = ehdr.e_entry.get(LE);
-    let load_offset = if assume_pic && e_entry < start_address {
-        // The kernel is assumed to contain PIC
-        start_address + load_offset
+    let phdrs = ehdr
+        .program_headers(LE, &reader)
+        .map_err(Error::InvalidProgramHeader)?;
+
+    // Determine the load offset by checking the lowest physical address in the program headers.
+    // For kernels with assume_pic=true, if the lowest load address is below start_address,
+    // we need to relocate the entire kernel upward. This handles both:
+    //
+    // 1. Old kernels (Linux < v6.17):
+    //    - Startup code is in .head.text at the beginning of .text
+    //    - Entry point is low, matches physical load address
+    //
+    // 2. New kernels (Linux v6.17+):
+    //    - Startup code moved to .init.text (commit: "x86/boot: Move startup code out of __head section", Linux v6.17)
+    //    - Entry point is high, but physical load address (from program headers) is still low
+    //
+    // This logic ensures both kernel layouts are relocated correctly if needed, based on the actual load address.
+    let load_offset = if assume_pic {
+        let mut lowest_paddr = u64::MAX;
+        for phdr in phdrs {
+            if phdr.p_type.get(LE) == elf::PT_LOAD {
+                let p_paddr = phdr.p_paddr.get(LE);
+                lowest_paddr = lowest_paddr.min(p_paddr);
+            }
+        }
+        if lowest_paddr < start_address {
+            // Kernel needs relocation: shift everything up so lowest_paddr aligns with start_address
+            start_address - lowest_paddr + load_offset
+        } else {
+            load_offset
+        }
     } else {
         load_offset
     };
@@ -155,10 +183,6 @@ where
         });
     }
 
-    let phdrs = ehdr
-        .program_headers(LE, &reader)
-        .map_err(Error::InvalidProgramHeader)?;
-
     // The first pass on the sections provides the layout data
     let (lowest_addr, last_offset, reloc_bias) = {
         let mut lowest_addr = u64::MAX;