kern: implement support for applying relr relocations

libraries/libmesosphere/include/mesosphere/init/kern_init_elf64.hpp

@@ -114,6 +114,23 @@ namespace ams::kern::init::Elf::Elf64 {
             }
     };
 
+    class Relr {
+        private:
+            Xword m_info;
+        public:
+            constexpr ALWAYS_INLINE bool IsLocation() const {
+                return (m_info & 1) == 0;
+            }
+
+            constexpr ALWAYS_INLINE Xword GetLocation() const {
+                return m_info;
+            }
+
+            constexpr ALWAYS_INLINE Xword GetBitmap() const {
+                return m_info >> 1;
+            }
+    };
+
     enum DynamicTag {
         DT_NULL    = 0,
         DT_RELA    = 7,
@@ -121,6 +138,10 @@ namespace ams::kern::init::Elf::Elf64 {
         DT_REL     = 17,
         DT_RELENT  = 19,
 
+        DT_RELRSZ  = 35,
+        DT_RELR    = 36,
+        DT_RELRENT = 37,
+
         DT_RELACOUNT = 0x6ffffff9,
         DT_RELCOUNT  = 0x6ffffffa
     };

libraries/libmesosphere/source/init/kern_init_elf.cpp

@@ -21,10 +21,13 @@ namespace ams::kern::init::Elf {
     void ApplyRelocations(uintptr_t base_address, const Dyn *dynamic) {
         uintptr_t dyn_rel    = 0;
         uintptr_t dyn_rela   = 0;
+        uintptr_t dyn_relr   = 0;
         uintptr_t rel_count  = 0;
         uintptr_t rela_count = 0;
+        uintptr_t relr_sz    = 0;
         uintptr_t rel_ent    = 0;
         uintptr_t rela_ent   = 0;
+        uintptr_t relr_ent   = 0;
 
         /* Iterate over all tags, identifying important extents. */
         for (const Dyn *cur_entry = dynamic; cur_entry->GetTag() != DT_NULL; cur_entry++) {
@@ -35,24 +38,38 @@ namespace ams::kern::init::Elf {
                 case DT_RELA:
                     dyn_rela   = base_address + cur_entry->GetPtr();
                     break;
+                case DT_RELR:
+                    dyn_relr   = base_address + cur_entry->GetPtr();
+                    break;
                 case DT_RELENT:
                     rel_ent    = cur_entry->GetValue();
                     break;
                 case DT_RELAENT:
                     rela_ent   = cur_entry->GetValue();
                     break;
+                case DT_RELRENT:
+                    relr_ent   = cur_entry->GetValue();
+                    break;
                 case DT_RELCOUNT:
                     rel_count  = cur_entry->GetValue();
                     break;
                 case DT_RELACOUNT:
                     rela_count = cur_entry->GetValue();
                     break;
+                case DT_RELRSZ:
+                    relr_sz    = cur_entry->GetValue();
+                    break;
             }
         }
 
         /* Apply all Rel relocations */
-        for (size_t i = 0; i < rel_count; i++) {
+        if (rel_count > 0) {
-            const auto &rel = *reinterpret_cast<const Elf::Rel *>(dyn_rel + rel_ent * i);
+            /* Check that the rel relocations are applyable. */
+            MESOSPHERE_INIT_ABORT_UNLESS(dyn_rel != 0);
+            MESOSPHERE_INIT_ABORT_UNLESS(rel_ent == sizeof(Elf::Rel));
+
+            for (size_t i = 0; i < rel_count; ++i) {
+                const auto &rel = reinterpret_cast<const Elf::Rel *>(dyn_rel)[i];
 
                 /* Only allow architecture-specific relocations. */
                 while (rel.GetType() != R_ARCHITECTURE_RELATIVE) { /* ... */ }
@@ -61,10 +78,16 @@ namespace ams::kern::init::Elf {
                 Elf::Addr *target_address = reinterpret_cast<Elf::Addr *>(base_address + rel.GetOffset());
                 *target_address += base_address;
             }
+        }
 
         /* Apply all Rela relocations. */
-        for (size_t i = 0; i < rela_count; i++) {
+        if (rela_count > 0) {
-            const auto &rela = *reinterpret_cast<const Elf::Rela *>(dyn_rela + rela_ent * i);
+            /* Check that the rela relocations are applyable. */
+            MESOSPHERE_INIT_ABORT_UNLESS(dyn_rela != 0);
+            MESOSPHERE_INIT_ABORT_UNLESS(rela_ent == sizeof(Elf::Rela));
+
+            for (size_t i = 0; i < rela_count; ++i) {
+                const auto &rela = reinterpret_cast<const Elf::Rela *>(dyn_rela)[i];
 
                 /* Only allow architecture-specific relocations. */
                 while (rela.GetType() != R_ARCHITECTURE_RELATIVE) { /* ... */ }
@@ -75,6 +98,42 @@ namespace ams::kern::init::Elf {
             }
         }
 
+        /* Apply all Relr relocations. */
+        if (relr_sz >= sizeof(Elf::Relr)) {
+            /* Check that the relr relocations are applyable. */
+            MESOSPHERE_INIT_ABORT_UNLESS(dyn_relr != 0);
+            MESOSPHERE_INIT_ABORT_UNLESS(relr_ent == sizeof(Elf::Relr));
+
+            const size_t relr_count = relr_sz / sizeof(Elf::Relr);
+
+            Elf::Addr *where = nullptr;
+            for (size_t i = 0; i < relr_count; ++i) {
+                const auto &relr = reinterpret_cast<const Elf::Relr *>(dyn_relr)[i];
+
+                if (relr.IsLocation()) {
+                    /* Update location. */
+                    where = reinterpret_cast<Elf::Addr *>(base_address + relr.GetLocation());
+
+                    /* Apply the relocation. */
+                    *(where++) += base_address;
+                } else {
+                    /* Get the bitmap. */
+                    u64 bitmap = relr.GetBitmap();
+
+                    /* Apply all relocations. */
+                    while (bitmap != 0) {
+                        const u64 next = util::CountTrailingZeros(bitmap);
+                        bitmap &= ~(static_cast<u64>(1) << next);
+                        where[next] += base_address;
+                    }
+
+                    /* Advance. */
+                    where += BITSIZEOF(bitmap) - 1;
+                }
+            }
+        }
+    }
+
     void CallInitArrayFuncs(uintptr_t init_array_start, uintptr_t init_array_end) {
         for (uintptr_t cur_entry = init_array_start; cur_entry < init_array_end; cur_entry += sizeof(void *)) {
             (*(void (**)())(cur_entry))();